diff --git a/Documentation/rest-api-changes.txt b/Documentation/rest-api-changes.txt
index 69bbc54..fb3e3ec 100644
--- a/Documentation/rest-api-changes.txt
+++ b/Documentation/rest-api-changes.txt
@@ -7757,7 +7757,7 @@
 have been granted `labelAs-NAME` permission for all keys of labels.
 |`reviewers`                           |optional|
 A list of link:rest-api-changes.html#reviewer-input[ReviewerInput]
-representing reviewers that should be added to the change.
+representing reviewers that should be added/removed to/from the change.
 |`ready`                               |optional|
 If true, and if the change is work in progress, then start review.
 It is an error for both `ready` and `work_in_progress` to be true.
@@ -7791,7 +7791,7 @@
 |`reviewers`              |optional|
 Map of account or group identifier to
 link:rest-api-changes.html#reviewer-result[ReviewerResult]
-representing the outcome of adding as a reviewer.
+representing the outcome of adding/removing a reviewer.
 Absent if no reviewer additions were requested.
 |`ready`                  |optional|
 If true, the change was moved from WIP to ready for review as a result of this
@@ -7822,24 +7822,25 @@
 
 [[reviewer-input]]
 === ReviewerInput
-The `ReviewerInput` entity contains information for adding a reviewer
-to a change.
+The `ReviewerInput` entity contains information for adding or removing
+reviewers to/from the change.
 
 [options="header",cols="1,^1,5"]
 |=============================
 |Field Name      ||Description
 |`reviewer`      ||
 The link:rest-api-accounts.html#account-id[ID] of one account that
-should be added as reviewer or the link:rest-api-groups.html#group-id[
+should be added/removed as reviewer or the link:rest-api-groups.html#group-id[
 ID] of one internal group for which all members should be added as reviewers. +
 If an ID identifies both an account and a group, only the account is
 added as reviewer to the change.
 External groups, such as LDAP groups, will be silently omitted from a
 link:#set-review[set-review] or
-link:rest-api-changes.html#add-reviewer[add-reviewer] call.
+link:rest-api-changes.html#add-reviewer[add-reviewer] call. A group can only be
+specified for adding reviewers, not for removing them.
 |`state`         |optional|
-Add reviewer in this state. Possible reviewer states are `REVIEWER`
-and `CC`. If not given, defaults to `REVIEWER`.
+Add reviewer in this state. Possible reviewer states are `REVIEWER`,
+`CC` and `REMOVED`. If not given, defaults to `REVIEWER`.
 |`confirmed`     |optional|
 Whether adding the reviewer is confirmed. +
 The Gerrit server may be configured to
@@ -7858,8 +7859,8 @@
 
 [[reviewer-result]]
 === ReviewerResult
-The `ReviewerResult` entity describes the result of adding a reviewer to a
-change.
+The `ReviewerResult` entity describes the result of modifying reviewers of
+a change.
 
 [options="header",cols="1,^1,5"]
 |===========================
@@ -7873,7 +7874,12 @@
 |`ccs`         |optional|
 The newly CCed accounts as a list of
 link:rest-api-accounts.html#account-info[AccountInfo] entities. This field will
-only appear if the requested `state` for the reviewer  was `CC`.
+only appear if the requested `state` for the reviewer was `CC`.
+|`removed`      |optional|
+The newly removed accounts as a list of
+link:rest-api-accounts.html#account-info[AccountInfo] entities.
+This field will only appear if the requested `state` for the reviewer was
+`REMOVED`.
 |`error`       |optional|
 Error message explaining why the reviewer could not be added. +
 If a group was specified in the input and an error is returned, it
diff --git a/java/com/google/gerrit/extensions/api/changes/ReviewInput.java b/java/com/google/gerrit/extensions/api/changes/ReviewInput.java
index 9da0d0f..87831e4 100644
--- a/java/com/google/gerrit/extensions/api/changes/ReviewInput.java
+++ b/java/com/google/gerrit/extensions/api/changes/ReviewInput.java
@@ -62,7 +62,7 @@
    */
   public String onBehalfOf;
 
-  /** Reviewers that should be added to this change. */
+  /** Reviewers that should be added to this change or removed from it. */
   public List<ReviewerInput> reviewers;
 
   /**
diff --git a/java/com/google/gerrit/extensions/api/changes/ReviewerResult.java b/java/com/google/gerrit/extensions/api/changes/ReviewerResult.java
index 324275a..1713674 100644
--- a/java/com/google/gerrit/extensions/api/changes/ReviewerResult.java
+++ b/java/com/google/gerrit/extensions/api/changes/ReviewerResult.java
@@ -18,17 +18,17 @@
 import com.google.gerrit.extensions.common.AccountInfo;
 import java.util.List;
 
-/** Result object representing the outcome of a request to add a reviewer. */
+/** Result object representing the outcome of a request to add/remove a reviewer. */
 public class ReviewerResult {
-  /** The identifier of an account or group that was to be added as a reviewer. */
+  /** The identifier of an account or group that was to be added/removed as a reviewer. */
   public String input;
 
-  /** If non-null, a string describing why the reviewer could not be added. */
+  /** If non-null, a string describing why the reviewer could not be added/removed. */
   @Nullable public String error;
 
   /**
    * Non-null and true if the reviewer cannot be added without explicit confirmation. This may be
-   * the case for groups of a certain size.
+   * the case for groups of a certain size. For removals, it's always false.
    */
   @Nullable public Boolean confirm;
 
@@ -39,11 +39,14 @@
   @Nullable public List<ReviewerInfo> reviewers;
 
   /**
-   * List of accounts CCed on the change. The size of this list may be greater than one (e.g. when a
-   * group is CCed). Null if no accounts were CCed or if reviewers is non-null.
+   * List of new accounts CCed on the change. The size of this list may be greater than one (e.g.
+   * when a group is CCed). Null if no accounts were CCed.
    */
   @Nullable public List<AccountInfo> ccs;
 
+  /** An account removed from the change. Null if no accounts were removed. */
+  @Nullable public AccountInfo removed;
+
   /**
    * Constructs a partially initialized result for the given reviewer.
    *
diff --git a/java/com/google/gerrit/server/change/AddReviewersOp.java b/java/com/google/gerrit/server/change/AddReviewersOp.java
index f79c9fc..1d6fb3c 100644
--- a/java/com/google/gerrit/server/change/AddReviewersOp.java
+++ b/java/com/google/gerrit/server/change/AddReviewersOp.java
@@ -23,7 +23,6 @@
 import static java.util.Objects.requireNonNull;
 import static java.util.stream.Collectors.toList;
 
-import com.google.auto.value.AutoValue;
 import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableSet;
 import com.google.common.collect.Lists;
@@ -31,7 +30,6 @@
 import com.google.gerrit.entities.Account;
 import com.google.gerrit.entities.Address;
 import com.google.gerrit.entities.Change;
-import com.google.gerrit.entities.PatchSet;
 import com.google.gerrit.entities.PatchSetApproval;
 import com.google.gerrit.extensions.client.ReviewerState;
 import com.google.gerrit.extensions.restapi.RestApiException;
@@ -42,7 +40,6 @@
 import com.google.gerrit.server.extensions.events.ReviewerAdded;
 import com.google.gerrit.server.notedb.ReviewerStateInternal;
 import com.google.gerrit.server.project.ProjectCache;
-import com.google.gerrit.server.update.BatchUpdateOp;
 import com.google.gerrit.server.update.ChangeContext;
 import com.google.gerrit.server.update.PostUpdateContext;
 import com.google.inject.Inject;
@@ -52,7 +49,7 @@
 import java.util.List;
 import java.util.Set;
 
-public class AddReviewersOp implements BatchUpdateOp {
+public class AddReviewersOp extends ReviewerOp {
   public interface Factory {
 
     /**
@@ -75,34 +72,6 @@
         boolean forGroup);
   }
 
-  @AutoValue
-  public abstract static class Result {
-    public abstract ImmutableList<PatchSetApproval> addedReviewers();
-
-    public abstract ImmutableList<Address> addedReviewersByEmail();
-
-    public abstract ImmutableList<Account.Id> addedCCs();
-
-    public abstract ImmutableList<Address> addedCCsByEmail();
-
-    static Builder builder() {
-      return new AutoValue_AddReviewersOp_Result.Builder();
-    }
-
-    @AutoValue.Builder
-    abstract static class Builder {
-      abstract Builder setAddedReviewers(Iterable<PatchSetApproval> addedReviewers);
-
-      abstract Builder setAddedReviewersByEmail(Iterable<Address> addedReviewersByEmail);
-
-      abstract Builder setAddedCCs(Iterable<Account.Id> addedCCs);
-
-      abstract Builder setAddedCCsByEmail(Iterable<Address> addedCCsByEmail);
-
-      abstract Result build();
-    }
-  }
-
   private final ApprovalsUtil approvalsUtil;
   private final PatchSetUtil psUtil;
   private final ReviewerAdded reviewerAdded;
@@ -121,10 +90,7 @@
   private Collection<Account.Id> addedCCs = ImmutableList.of();
   private Collection<Address> addedCCsByEmail = ImmutableList.of();
 
-  private boolean sendEmail = true;
   private Change change;
-  private PatchSet patchSet;
-  private Result opResult;
 
   @Inject
   AddReviewersOp(
@@ -152,17 +118,6 @@
     this.forGroup = forGroup;
   }
 
-  // TODO(dborowitz): This mutable setter is ugly, but a) it's less ugly than adding boolean args
-  // all the way through the constructor stack, and b) this class is slated to be completely
-  // rewritten.
-  public void suppressEmail() {
-    this.sendEmail = false;
-  }
-
-  void setPatchSet(PatchSet patchSet) {
-    this.patchSet = requireNonNull(patchSet);
-  }
-
   @Override
   public boolean updateChange(ChangeContext ctx) throws RestApiException, IOException {
     change = ctx.getChange();
@@ -252,8 +207,10 @@
           change,
           Lists.transform(addedReviewers, PatchSetApproval::accountId),
           addedCCs,
+          ImmutableSet.of(),
           addedReviewersByEmail,
           addedCCsByEmail,
+          ImmutableSet.of(),
           ctx.getNotify(change.getId()));
     }
     if (!addedReviewers.isEmpty()) {
@@ -266,9 +223,4 @@
           ctx.getChangeData(change), patchSet, reviewers, ctx.getAccount(), ctx.getWhen());
     }
   }
-
-  public Result getResult() {
-    checkState(opResult != null, "Batch update wasn't executed yet");
-    return opResult;
-  }
 }
diff --git a/java/com/google/gerrit/server/change/ChangeMessages.java b/java/com/google/gerrit/server/change/ChangeMessages.java
index 6f2e1ef..787f036 100644
--- a/java/com/google/gerrit/server/change/ChangeMessages.java
+++ b/java/com/google/gerrit/server/change/ChangeMessages.java
@@ -31,6 +31,7 @@
   public String reviewerInvalid;
   public String reviewerNotFoundUserOrGroup;
 
+  public String groupRemovalIsNotAllowed;
   public String groupIsNotAllowed;
   public String groupHasTooManyMembers;
   public String groupManyMembersConfirmation;
diff --git a/java/com/google/gerrit/server/change/DeleteReviewerByEmailOp.java b/java/com/google/gerrit/server/change/DeleteReviewerByEmailOp.java
index 2505024..839d7f1 100644
--- a/java/com/google/gerrit/server/change/DeleteReviewerByEmailOp.java
+++ b/java/com/google/gerrit/server/change/DeleteReviewerByEmailOp.java
@@ -22,14 +22,13 @@
 import com.google.gerrit.server.ChangeUtil;
 import com.google.gerrit.server.mail.send.DeleteReviewerSender;
 import com.google.gerrit.server.mail.send.MessageIdGenerator;
-import com.google.gerrit.server.update.BatchUpdateOp;
 import com.google.gerrit.server.update.ChangeContext;
 import com.google.gerrit.server.update.PostUpdateContext;
 import com.google.inject.Inject;
 import com.google.inject.assistedinject.Assisted;
 import java.util.Collections;
 
-public class DeleteReviewerByEmailOp implements BatchUpdateOp {
+public class DeleteReviewerByEmailOp extends ReviewerOp {
   private static final FluentLogger logger = FluentLogger.forEnclosingClass();
 
   public interface Factory {
@@ -74,22 +73,25 @@
 
   @Override
   public void postUpdate(PostUpdateContext ctx) {
-    try {
-      NotifyResolver.Result notify = ctx.getNotify(change.getId());
-      if (!notify.shouldNotify()) {
-        return;
+    opResult = Result.builder().setDeletedReviewerByEmail(reviewer).build();
+    if (sendEmail) {
+      try {
+        NotifyResolver.Result notify = ctx.getNotify(change.getId());
+        if (!notify.shouldNotify()) {
+          return;
+        }
+        DeleteReviewerSender emailSender =
+            deleteReviewerSenderFactory.create(ctx.getProject(), change.getId());
+        emailSender.setFrom(ctx.getAccountId());
+        emailSender.addReviewersByEmail(Collections.singleton(reviewer));
+        emailSender.setChangeMessage(changeMessage.getMessage(), changeMessage.getWrittenOn());
+        emailSender.setNotify(notify);
+        emailSender.setMessageId(
+            messageIdGenerator.fromChangeUpdate(ctx.getRepoView(), change.currentPatchSetId()));
+        emailSender.send();
+      } catch (Exception err) {
+        logger.atSevere().withCause(err).log("Cannot email update for change %s", change.getId());
       }
-      DeleteReviewerSender emailSender =
-          deleteReviewerSenderFactory.create(ctx.getProject(), change.getId());
-      emailSender.setFrom(ctx.getAccountId());
-      emailSender.addReviewersByEmail(Collections.singleton(reviewer));
-      emailSender.setChangeMessage(changeMessage.getMessage(), changeMessage.getWrittenOn());
-      emailSender.setNotify(notify);
-      emailSender.setMessageId(
-          messageIdGenerator.fromChangeUpdate(ctx.getRepoView(), change.currentPatchSetId()));
-      emailSender.send();
-    } catch (Exception err) {
-      logger.atSevere().withCause(err).log("Cannot email update for change %s", change.getId());
     }
   }
 }
diff --git a/java/com/google/gerrit/server/change/DeleteReviewerOp.java b/java/com/google/gerrit/server/change/DeleteReviewerOp.java
index b1fc67d..095a19b 100644
--- a/java/com/google/gerrit/server/change/DeleteReviewerOp.java
+++ b/java/com/google/gerrit/server/change/DeleteReviewerOp.java
@@ -23,7 +23,6 @@
 import com.google.gerrit.entities.ChangeMessage;
 import com.google.gerrit.entities.LabelType;
 import com.google.gerrit.entities.LabelTypes;
-import com.google.gerrit.entities.PatchSet;
 import com.google.gerrit.entities.PatchSetApproval;
 import com.google.gerrit.entities.Project;
 import com.google.gerrit.exceptions.EmailException;
@@ -35,6 +34,7 @@
 import com.google.gerrit.server.ChangeMessagesUtil;
 import com.google.gerrit.server.IdentifiedUser;
 import com.google.gerrit.server.PatchSetUtil;
+import com.google.gerrit.server.account.AccountCache;
 import com.google.gerrit.server.account.AccountState;
 import com.google.gerrit.server.extensions.events.ReviewerDeleted;
 import com.google.gerrit.server.mail.send.DeleteReviewerSender;
@@ -44,7 +44,6 @@
 import com.google.gerrit.server.permissions.PermissionBackendException;
 import com.google.gerrit.server.project.ProjectCache;
 import com.google.gerrit.server.project.RemoveReviewerControl;
-import com.google.gerrit.server.update.BatchUpdateOp;
 import com.google.gerrit.server.update.ChangeContext;
 import com.google.gerrit.server.update.PostUpdateContext;
 import com.google.gerrit.server.update.RepoView;
@@ -56,11 +55,11 @@
 import java.util.HashMap;
 import java.util.Map;
 
-public class DeleteReviewerOp implements BatchUpdateOp {
+public class DeleteReviewerOp extends ReviewerOp {
   private static final FluentLogger logger = FluentLogger.forEnclosingClass();
 
   public interface Factory {
-    DeleteReviewerOp create(AccountState reviewerAccount, DeleteReviewerInput input);
+    DeleteReviewerOp create(Account reviewerAccount, DeleteReviewerInput input);
   }
 
   private final ApprovalsUtil approvalsUtil;
@@ -73,13 +72,13 @@
   private final RemoveReviewerControl removeReviewerControl;
   private final ProjectCache projectCache;
   private final MessageIdGenerator messageIdGenerator;
+  private final AccountCache accountCache;
 
-  private final AccountState reviewer;
+  private final Account reviewer;
   private final DeleteReviewerInput input;
 
   ChangeMessage changeMessage;
   Change currChange;
-  PatchSet currPs;
   Map<String, Short> newApprovals = new HashMap<>();
   Map<String, Short> oldApprovals = new HashMap<>();
 
@@ -95,7 +94,8 @@
       RemoveReviewerControl removeReviewerControl,
       ProjectCache projectCache,
       MessageIdGenerator messageIdGenerator,
-      @Assisted AccountState reviewerAccount,
+      AccountCache accountCache,
+      @Assisted Account reviewerAccount,
       @Assisted DeleteReviewerInput input) {
     this.approvalsUtil = approvalsUtil;
     this.psUtil = psUtil;
@@ -107,6 +107,7 @@
     this.removeReviewerControl = removeReviewerControl;
     this.projectCache = projectCache;
     this.messageIdGenerator = messageIdGenerator;
+    this.accountCache = accountCache;
     this.reviewer = reviewerAccount;
     this.input = input;
   }
@@ -114,15 +115,18 @@
   @Override
   public boolean updateChange(ChangeContext ctx)
       throws AuthException, ResourceNotFoundException, PermissionBackendException, IOException {
-    Account.Id reviewerId = reviewer.account().id();
+    Account.Id reviewerId = reviewer.id();
     // Check of removing this reviewer (even if there is no vote processed by the loop below) is OK
     removeReviewerControl.checkRemoveReviewer(ctx.getNotes(), ctx.getUser(), reviewerId);
 
     if (!approvalsUtil.getReviewers(ctx.getNotes()).all().contains(reviewerId)) {
-      throw new ResourceNotFoundException();
+      throw new ResourceNotFoundException(
+          String.format(
+              "Reviewer %s doesn't exist in the change, hence can't delete it",
+              reviewer.getName()));
     }
     currChange = ctx.getChange();
-    currPs = psUtil.current(ctx.getNotes());
+    setPatchSet(psUtil.current(ctx.getNotes()));
 
     LabelTypes labelTypes =
         projectCache
@@ -141,14 +145,14 @@
             ? "cc"
             : "reviewer";
     StringBuilder msg = new StringBuilder();
-    msg.append(String.format("Removed %s %s", ccOrReviewer, reviewer.account().fullName()));
+    msg.append(String.format("Removed %s %s", ccOrReviewer, reviewer.fullName()));
     StringBuilder removedVotesMsg = new StringBuilder();
     removedVotesMsg.append(" with the following votes:\n\n");
     boolean votesRemoved = false;
     for (PatchSetApproval a : approvals(ctx, reviewerId)) {
       // Check if removing this vote is OK
       removeReviewerControl.checkRemoveReviewer(ctx.getNotes(), ctx.getUser(), a);
-      if (a.patchSetId().equals(currPs.id()) && a.value() != 0) {
+      if (a.patchSetId().equals(patchSet.id()) && a.value() != 0) {
         oldApprovals.put(a.label(), a.value());
         removedVotesMsg
             .append("* ")
@@ -166,7 +170,7 @@
     } else {
       msg.append(".");
     }
-    ChangeUpdate update = ctx.getUpdate(currPs.id());
+    ChangeUpdate update = ctx.getUpdate(patchSet.id());
     update.removeReviewer(reviewerId);
 
     changeMessage =
@@ -178,26 +182,31 @@
 
   @Override
   public void postUpdate(PostUpdateContext ctx) {
+    opResult = Result.builder().setDeletedReviewer(reviewer.id()).build();
+
     NotifyResolver.Result notify = ctx.getNotify(currChange.getId());
-    if (input.notify == null
-        && currChange.isWorkInProgress()
-        && !oldApprovals.isEmpty()
-        && notify.handling().compareTo(NotifyHandling.OWNER) < 0) {
-      // Override NotifyHandling from the context to notify owner if votes were removed on a WIP
-      // change.
-      notify = notify.withHandling(NotifyHandling.OWNER);
-    }
-    try {
-      if (notify.shouldNotify()) {
-        emailReviewers(ctx.getProject(), currChange, changeMessage, notify, ctx.getRepoView());
+    if (sendEmail) {
+      if (input.notify == null
+          && currChange.isWorkInProgress()
+          && !oldApprovals.isEmpty()
+          && notify.handling().compareTo(NotifyHandling.OWNER) < 0) {
+        // Override NotifyHandling from the context to notify owner if votes were removed on a WIP
+        // change.
+        notify = notify.withHandling(NotifyHandling.OWNER);
       }
-    } catch (Exception err) {
-      logger.atSevere().withCause(err).log("Cannot email update for change %s", currChange.getId());
+      try {
+        if (notify.shouldNotify()) {
+          emailReviewers(ctx.getProject(), currChange, changeMessage, notify, ctx.getRepoView());
+        }
+      } catch (Exception err) {
+        logger.atSevere().withCause(err).log(
+            "Cannot email update for change %s", currChange.getId());
+      }
     }
     reviewerDeleted.fire(
         ctx.getChangeData(currChange),
-        currPs,
-        reviewer,
+        patchSet,
+        accountCache.get(reviewer.id()).orElse(AccountState.forAccount(reviewer)),
         ctx.getAccount(),
         changeMessage.getMessage(),
         newApprovals,
@@ -227,14 +236,14 @@
       RepoView repoView)
       throws EmailException {
     Account.Id userId = user.get().getAccountId();
-    if (userId.equals(reviewer.account().id())) {
+    if (userId.equals(reviewer.id())) {
       // The user knows they removed themselves, don't bother emailing them.
       return;
     }
     DeleteReviewerSender emailSender =
         deleteReviewerSenderFactory.create(projectName, change.getId());
     emailSender.setFrom(userId);
-    emailSender.addReviewers(Collections.singleton(reviewer.account().id()));
+    emailSender.addReviewers(Collections.singleton(reviewer.id()));
     emailSender.setChangeMessage(changeMessage.getMessage(), changeMessage.getWrittenOn());
     emailSender.setNotify(notify);
     emailSender.setMessageId(
diff --git a/java/com/google/gerrit/server/change/DeleteReviewersUtil.java b/java/com/google/gerrit/server/change/DeleteReviewersUtil.java
new file mode 100644
index 0000000..a4f306b
--- /dev/null
+++ b/java/com/google/gerrit/server/change/DeleteReviewersUtil.java
@@ -0,0 +1,85 @@
+// Copyright (C) 2021 The Android Open Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package com.google.gerrit.server.change;
+
+import com.google.gerrit.entities.Account;
+import com.google.gerrit.entities.Address;
+import com.google.gerrit.extensions.api.changes.DeleteReviewerInput;
+import com.google.gerrit.extensions.api.changes.ReviewerInput;
+import com.google.gerrit.extensions.restapi.AuthException;
+import com.google.gerrit.extensions.restapi.ResourceNotFoundException;
+import com.google.gerrit.server.ApprovalsUtil;
+import com.google.gerrit.server.account.AccountResolver;
+import com.google.gerrit.server.notedb.ChangeNotes;
+import com.google.gerrit.server.update.BatchUpdate;
+import com.google.inject.Inject;
+import java.io.IOException;
+import java.util.Collection;
+import org.eclipse.jgit.errors.ConfigInvalidException;
+
+public class DeleteReviewersUtil {
+  private final DeleteReviewerOp.Factory deleteReviewerOpFactory;
+  private final DeleteReviewerByEmailOp.Factory deleteReviewerByEmailOpFactory;
+  private final AccountResolver accountResolver;
+  private final ApprovalsUtil approvalsUtil;
+
+  @Inject
+  DeleteReviewersUtil(
+      DeleteReviewerOp.Factory deleteReviewerOpFactory,
+      DeleteReviewerByEmailOp.Factory deleteReviewerByEmailOpFactory,
+      AccountResolver accountResolver,
+      ApprovalsUtil approvalsUtil) {
+    this.deleteReviewerOpFactory = deleteReviewerOpFactory;
+    this.deleteReviewerByEmailOpFactory = deleteReviewerByEmailOpFactory;
+    this.accountResolver = accountResolver;
+    this.approvalsUtil = approvalsUtil;
+  }
+
+  public void addDeleteReviewerOpToBatchUpdate(
+      BatchUpdate batchUpdate, ChangeNotes changeNotes, ReviewerInput reviewerInput)
+      throws IOException, ConfigInvalidException, AuthException, ResourceNotFoundException {
+
+    try {
+      AccountResolver.Result result =
+          accountResolver.resolveIgnoreVisibility(reviewerInput.reviewer);
+      if (fetchAccountIds(changeNotes).contains(result.asUniqueUser().getAccountId())) {
+        DeleteReviewerInput deleteReviewerInput = new DeleteReviewerInput();
+        deleteReviewerInput.notify = reviewerInput.notify;
+        deleteReviewerInput.notifyDetails = reviewerInput.notifyDetails;
+        batchUpdate.addOp(
+            changeNotes.getChangeId(),
+            deleteReviewerOpFactory.create(result.asUnique().account(), deleteReviewerInput));
+        return;
+      } else {
+        return;
+      }
+    } catch (AccountResolver.UnresolvableAccountException e) {
+      if (e.isSelf()) {
+        throw new AuthException(e.getMessage(), e);
+      }
+    }
+    Address address = Address.tryParse(reviewerInput.reviewer);
+    if (address != null && changeNotes.getReviewersByEmail().all().contains(address)) {
+      batchUpdate.addOp(changeNotes.getChangeId(), deleteReviewerByEmailOpFactory.create(address));
+      return;
+    }
+
+    throw new ResourceNotFoundException(reviewerInput.reviewer);
+  }
+
+  private Collection<Account.Id> fetchAccountIds(ChangeNotes changeNotes) {
+    return approvalsUtil.getReviewers(changeNotes).all();
+  }
+}
diff --git a/java/com/google/gerrit/server/change/ModifyReviewersEmail.java b/java/com/google/gerrit/server/change/ModifyReviewersEmail.java
index a7327f6..cb747f6 100644
--- a/java/com/google/gerrit/server/change/ModifyReviewersEmail.java
+++ b/java/com/google/gerrit/server/change/ModifyReviewersEmail.java
@@ -55,19 +55,25 @@
       Change change,
       Collection<Account.Id> added,
       Collection<Account.Id> copied,
+      Collection<Account.Id> removed,
       Collection<Address> addedByEmail,
       Collection<Address> copiedByEmail,
+      Collection<Address> removedByEmail,
       NotifyResolver.Result notify) {
-    // The user knows they added themselves, don't bother emailing them.
+    // The user knows they added/removed themselves, don't bother emailing them.
     Account.Id userId = user.getAccountId();
     ImmutableList<Account.Id> immutableToMail =
         added.stream().filter(id -> !id.equals(userId)).collect(toImmutableList());
     ImmutableList<Account.Id> immutableToCopy =
         copied.stream().filter(id -> !id.equals(userId)).collect(toImmutableList());
+    ImmutableList<Account.Id> immutableToRemove =
+        removed.stream().filter(id -> !id.equals(userId)).collect(toImmutableList());
     if (immutableToMail.isEmpty()
         && immutableToCopy.isEmpty()
+        && immutableToRemove.isEmpty()
         && addedByEmail.isEmpty()
-        && copiedByEmail.isEmpty()) {
+        && copiedByEmail.isEmpty()
+        && removedByEmail.isEmpty()) {
       return;
     }
 
@@ -77,6 +83,7 @@
     Project.NameKey projectNameKey = change.getProject();
     ImmutableList<Address> immutableAddedByEmail = ImmutableList.copyOf(addedByEmail);
     ImmutableList<Address> immutableCopiedByEmail = ImmutableList.copyOf(copiedByEmail);
+    ImmutableList<Address> immutableRemovedByEmail = ImmutableList.copyOf(removedByEmail);
 
     @SuppressWarnings("unused")
     Future<?> possiblyIgnoredError =
@@ -91,6 +98,8 @@
                 emailSender.addReviewersByEmail(immutableAddedByEmail);
                 emailSender.addExtraCC(immutableToCopy);
                 emailSender.addExtraCCByEmail(immutableCopiedByEmail);
+                emailSender.addRemovedReviewers(immutableToRemove);
+                emailSender.addRemovedByEmailReviewers(immutableRemovedByEmail);
                 emailSender.setMessageId(
                     messageIdGenerator.fromChangeUpdate(
                         change.getProject(), change.currentPatchSetId()));
diff --git a/java/com/google/gerrit/server/change/ReviewerModifier.java b/java/com/google/gerrit/server/change/ReviewerModifier.java
index b45b6a9..6f05072 100644
--- a/java/com/google/gerrit/server/change/ReviewerModifier.java
+++ b/java/com/google/gerrit/server/change/ReviewerModifier.java
@@ -19,12 +19,14 @@
 import static com.google.common.collect.ImmutableList.toImmutableList;
 import static com.google.common.collect.ImmutableSet.toImmutableSet;
 import static com.google.gerrit.extensions.client.ReviewerState.CC;
+import static com.google.gerrit.extensions.client.ReviewerState.REMOVED;
 import static com.google.gerrit.server.project.ProjectCache.illegalState;
 import static java.util.Comparator.comparing;
 import static java.util.Objects.requireNonNull;
 
 import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableSet;
+import com.google.common.collect.Iterables;
 import com.google.common.collect.Lists;
 import com.google.common.collect.Ordering;
 import com.google.common.collect.Streams;
@@ -39,6 +41,7 @@
 import com.google.gerrit.entities.GroupDescription;
 import com.google.gerrit.entities.PatchSet;
 import com.google.gerrit.entities.PatchSetApproval;
+import com.google.gerrit.extensions.api.changes.DeleteReviewerInput;
 import com.google.gerrit.extensions.api.changes.NotifyHandling;
 import com.google.gerrit.extensions.api.changes.ReviewerInfo;
 import com.google.gerrit.extensions.api.changes.ReviewerInput;
@@ -155,6 +158,8 @@
   private final Provider<AnonymousUser> anonymousProvider;
   private final AddReviewersOp.Factory addReviewersOpFactory;
   private final OutgoingEmailValidator validator;
+  private final DeleteReviewerOp.Factory deleteReviewerOpFactory;
+  private final DeleteReviewerByEmailOp.Factory deleteReviewerByEmailOpFactory;
 
   @Inject
   ReviewerModifier(
@@ -168,7 +173,9 @@
       ProjectCache projectCache,
       Provider<AnonymousUser> anonymousProvider,
       AddReviewersOp.Factory addReviewersOpFactory,
-      OutgoingEmailValidator validator) {
+      OutgoingEmailValidator validator,
+      DeleteReviewerOp.Factory deleteReviewerOpFactory,
+      DeleteReviewerByEmailOp.Factory deleteReviewerByEmailOpFactory) {
     this.accountResolver = accountResolver;
     this.permissionBackend = permissionBackend;
     this.groupResolver = groupResolver;
@@ -180,6 +187,8 @@
     this.anonymousProvider = anonymousProvider;
     this.addReviewersOpFactory = addReviewersOpFactory;
     this.validator = validator;
+    this.deleteReviewerOpFactory = deleteReviewerOpFactory;
+    this.deleteReviewerByEmailOpFactory = deleteReviewerByEmailOpFactory;
   }
 
   /**
@@ -209,7 +218,7 @@
               .orElseThrow(illegalState(notes.getProjectName()))
               .is(BooleanProjectConfig.ENABLE_REVIEWER_BY_EMAIL);
 
-      ReviewerModification byAccountId = addByAccountId(input, notes, user);
+      ReviewerModification byAccountId = byAccountId(input, notes, user);
 
       ReviewerModification wholeGroup = null;
       if (!byAccountId.exactMatchFound) {
@@ -244,15 +253,14 @@
         newReviewerInput(user.getUserName().orElse(null), CC, NotifyHandling.NONE),
         revision.getNotes(),
         revision.getUser(),
-        ImmutableSet.of(user.getAccountId()),
+        ImmutableSet.of(user.asIdentifiedUser().getAccount()),
         null,
         true,
         false);
   }
 
   @Nullable
-  private ReviewerModification addByAccountId(
-      ReviewerInput input, ChangeNotes notes, CurrentUser user)
+  private ReviewerModification byAccountId(ReviewerInput input, ChangeNotes notes, CurrentUser user)
       throws PermissionBackendException, IOException, ConfigInvalidException {
     IdentifiedUser reviewerUser;
     boolean exactMatchFound = false;
@@ -273,7 +281,7 @@
           input,
           notes,
           user,
-          ImmutableSet.of(reviewerUser.getAccountId()),
+          ImmutableSet.of(reviewerUser.getAccount()),
           null,
           exactMatchFound,
           false);
@@ -319,7 +327,14 @@
           MessageFormat.format(ChangeMessages.get().groupIsNotAllowed, group.getName()));
     }
 
-    Set<Account.Id> reviewers = new HashSet<>();
+    if (input.state().equals(REMOVED)) {
+      return fail(
+          input,
+          FailureType.OTHER,
+          MessageFormat.format(ChangeMessages.get().groupRemovalIsNotAllowed, group.getName()));
+    }
+
+    Set<Account> reviewers = new HashSet<>();
     Set<Account> members;
     try {
       members = groupMembers.listAccounts(group.getGroupUUID(), notes.getProjectName());
@@ -356,7 +371,7 @@
 
     for (Account member : members) {
       if (isValidReviewer(notes.getChange().getDest(), member)) {
-        reviewers.add(member.id());
+        reviewers.add(member);
       }
     }
 
@@ -412,8 +427,8 @@
 
   public class ReviewerModification {
     public final ReviewerResult result;
-    @Nullable public final AddReviewersOp op;
-    public final ImmutableSet<Account.Id> reviewers;
+    @Nullable public final ReviewerOp op;
+    public final ImmutableSet<Account> reviewers;
     public final ImmutableSet<Address> reviewersByEmail;
     @Nullable final IdentifiedUser caller;
     final boolean exactMatchFound;
@@ -435,7 +450,7 @@
         ReviewerInput input,
         ChangeNotes notes,
         CurrentUser caller,
-        @Nullable Iterable<Account.Id> reviewers,
+        @Nullable Iterable<Account> reviewers,
         @Nullable Iterable<Address> reviewersByEmail,
         boolean exactMatchFound,
         boolean forGroup) {
@@ -452,14 +467,40 @@
       this.reviewersByEmail =
           reviewersByEmail == null ? ImmutableSet.of() : ImmutableSet.copyOf(reviewersByEmail);
       this.caller = caller.asIdentifiedUser();
-      op = addReviewersOpFactory.create(this.reviewers, this.reviewersByEmail, state(), forGroup);
+      if (state().equals(REMOVED)) {
+        // only one is set.
+        checkState(
+            (this.reviewers.size() == 1 && this.reviewersByEmail.isEmpty())
+                || (this.reviewers.isEmpty() && this.reviewersByEmail.size() == 1));
+        if (this.reviewers.size() >= 1) {
+          checkState(this.reviewers.size() == 1);
+          DeleteReviewerInput deleteReviewerInput = new DeleteReviewerInput();
+          deleteReviewerInput.notify = input.notify;
+          deleteReviewerInput.notifyDetails = input.notifyDetails;
+          op =
+              deleteReviewerOpFactory.create(
+                  Iterables.getOnlyElement(this.reviewers.asList()), deleteReviewerInput);
+        } else {
+          checkState(this.reviewersByEmail.size() == 1);
+          op =
+              deleteReviewerByEmailOpFactory.create(
+                  Iterables.getOnlyElement(this.reviewersByEmail.asList()));
+        }
+      } else {
+        op =
+            addReviewersOpFactory.create(
+                this.reviewers.stream().map(Account::id).collect(toImmutableSet()),
+                this.reviewersByEmail,
+                state(),
+                forGroup);
+      }
       this.exactMatchFound = exactMatchFound;
     }
 
-    private ImmutableSet<Account.Id> omitOwner(ChangeNotes notes, Iterable<Account.Id> reviewers) {
+    private ImmutableSet<Account> omitOwner(ChangeNotes notes, Iterable<Account> reviewers) {
       return reviewers != null
           ? Streams.stream(reviewers)
-              .filter(id -> !id.equals(notes.getChange().getOwner()))
+              .filter(account -> !account.id().equals(notes.getChange().getOwner()))
               .collect(toImmutableSet())
           : ImmutableSet.of();
     }
@@ -470,31 +511,52 @@
 
       // Generate result details and fill AccountLoader. This occurs outside
       // the Op because the accounts are in a different table.
-      AddReviewersOp.Result opResult = op.getResult();
-      if (state() == CC) {
-        result.ccs = Lists.newArrayListWithCapacity(opResult.addedCCs().size());
-        for (Account.Id accountId : opResult.addedCCs()) {
-          result.ccs.add(json.format(new ReviewerInfo(accountId.get()), accountId, cd));
-        }
-        accountLoaderFactory.create(true).fill(result.ccs);
-        for (Address a : opResult.addedCCsByEmail()) {
-          result.ccs.add(new AccountInfo(a.name(), a.email()));
-        }
-      } else {
-        result.reviewers = Lists.newArrayListWithCapacity(opResult.addedReviewers().size());
-        for (PatchSetApproval psa : opResult.addedReviewers()) {
-          // New reviewers have value 0, don't bother normalizing.
-          result.reviewers.add(
-              json.format(
-                  new ReviewerInfo(psa.accountId().get()),
-                  psa.accountId(),
-                  cd,
-                  ImmutableList.of(psa)));
-        }
-        accountLoaderFactory.create(true).fill(result.reviewers);
-        for (Address a : opResult.addedReviewersByEmail()) {
-          result.reviewers.add(ReviewerInfo.byEmail(a.name(), a.email()));
-        }
+      ReviewerOp.Result opResult = op.getResult();
+      switch (state()) {
+        case CC:
+          result.ccs = Lists.newArrayListWithCapacity(opResult.addedCCs().size());
+          for (Account.Id accountId : opResult.addedCCs()) {
+            result.ccs.add(json.format(new ReviewerInfo(accountId.get()), accountId, cd));
+          }
+          accountLoaderFactory.create(true).fill(result.ccs);
+          for (Address a : opResult.addedCCsByEmail()) {
+            result.ccs.add(new AccountInfo(a.name(), a.email()));
+          }
+          break;
+        case REVIEWER:
+          result.reviewers = Lists.newArrayListWithCapacity(opResult.addedReviewers().size());
+          for (PatchSetApproval psa : opResult.addedReviewers()) {
+            // New reviewers have value 0, don't bother normalizing.
+            result.reviewers.add(
+                json.format(
+                    new ReviewerInfo(psa.accountId().get()),
+                    psa.accountId(),
+                    cd,
+                    ImmutableList.of(psa)));
+          }
+          accountLoaderFactory.create(true).fill(result.reviewers);
+          for (Address a : opResult.addedReviewersByEmail()) {
+            result.reviewers.add(ReviewerInfo.byEmail(a.name(), a.email()));
+          }
+          break;
+        case REMOVED:
+          if (opResult.deletedReviewer().isPresent()) {
+            result.removed =
+                json.format(
+                    new ReviewerInfo(opResult.deletedReviewer().get().get()),
+                    opResult.deletedReviewer().get(),
+                    cd);
+            accountLoaderFactory.create(true).fill(ImmutableList.of(result.removed));
+          } else if (opResult.deletedReviewerByEmail().isPresent()) {
+            result.removed =
+                new AccountInfo(
+                    opResult.deletedReviewerByEmail().get().name(),
+                    opResult.deletedReviewerByEmail().get().email());
+          }
+          break;
+        default:
+          throw new IllegalStateException(
+              String.format("Illegal ReviewerState argument is %s", state().name()));
       }
     }
 
@@ -573,7 +635,7 @@
     // We never call updateRepo on the addition ops, which is only ok because it's a no-op.
 
     public void updateChange(ChangeContext ctx, PatchSet patchSet)
-        throws RestApiException, IOException {
+        throws RestApiException, IOException, PermissionBackendException {
       for (ReviewerModification addition : modifications()) {
         addition.op.setPatchSet(patchSet);
         addition.op.updateChange(ctx);
diff --git a/java/com/google/gerrit/server/change/ReviewerOp.java b/java/com/google/gerrit/server/change/ReviewerOp.java
new file mode 100644
index 0000000..716ac5e
--- /dev/null
+++ b/java/com/google/gerrit/server/change/ReviewerOp.java
@@ -0,0 +1,99 @@
+// Copyright (C) 2021 The Android Open Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package com.google.gerrit.server.change;
+
+import static com.google.common.base.Preconditions.checkState;
+import static java.util.Objects.requireNonNull;
+
+import com.google.auto.value.AutoValue;
+import com.google.common.collect.ImmutableList;
+import com.google.gerrit.entities.Account;
+import com.google.gerrit.entities.Address;
+import com.google.gerrit.entities.PatchSet;
+import com.google.gerrit.entities.PatchSetApproval;
+import com.google.gerrit.extensions.restapi.RestApiException;
+import com.google.gerrit.server.permissions.PermissionBackendException;
+import com.google.gerrit.server.update.BatchUpdateOp;
+import com.google.gerrit.server.update.ChangeContext;
+import java.io.IOException;
+import java.util.Optional;
+
+public class ReviewerOp implements BatchUpdateOp {
+  protected boolean sendEmail = true;
+  protected PatchSet patchSet;
+  protected Result opResult;
+
+  // TODO(dborowitz): This mutable setter is ugly, but a) it's less ugly than adding boolean args
+  // all the way through the constructor stack, and b) this class is slated to be completely
+  // rewritten.
+  public void suppressEmail() {
+    this.sendEmail = false;
+  }
+
+  void setPatchSet(PatchSet patchSet) {
+    this.patchSet = requireNonNull(patchSet);
+  }
+
+  @AutoValue
+  public abstract static class Result {
+    public abstract ImmutableList<PatchSetApproval> addedReviewers();
+
+    public abstract ImmutableList<Address> addedReviewersByEmail();
+
+    public abstract ImmutableList<Account.Id> addedCCs();
+
+    public abstract ImmutableList<Address> addedCCsByEmail();
+
+    public abstract Optional<Account.Id> deletedReviewer();
+
+    public abstract Optional<Address> deletedReviewerByEmail();
+
+    static Builder builder() {
+      return new AutoValue_ReviewerOp_Result.Builder()
+          .setAddedReviewers(ImmutableList.of())
+          .setAddedReviewersByEmail(ImmutableList.of())
+          .setAddedCCs(ImmutableList.of())
+          .setAddedCCsByEmail(ImmutableList.of());
+    }
+
+    @AutoValue.Builder
+    abstract static class Builder {
+      abstract Builder setAddedReviewers(Iterable<PatchSetApproval> addedReviewers);
+
+      abstract Builder setAddedReviewersByEmail(Iterable<Address> addedReviewersByEmail);
+
+      abstract Builder setAddedCCs(Iterable<Account.Id> addedCCs);
+
+      abstract Builder setAddedCCsByEmail(Iterable<Address> addedCCsByEmail);
+
+      abstract Builder setDeletedReviewerByEmail(Address deletedReviewerByEmail);
+
+      abstract Builder setDeletedReviewer(Account.Id deletedReviewer);
+
+      abstract Result build();
+    }
+  }
+
+  public Result getResult() {
+    checkState(opResult != null, "Batch update wasn't executed yet");
+    return opResult;
+  }
+
+  @Override
+  public boolean updateChange(ChangeContext ctx)
+      throws RestApiException, IOException, PermissionBackendException {
+    return false;
+  }
+}
diff --git a/java/com/google/gerrit/server/mail/send/NewChangeSender.java b/java/com/google/gerrit/server/mail/send/NewChangeSender.java
index ee9a328..001de52 100644
--- a/java/com/google/gerrit/server/mail/send/NewChangeSender.java
+++ b/java/com/google/gerrit/server/mail/send/NewChangeSender.java
@@ -31,6 +31,8 @@
   private final Set<Address> reviewersByEmail = new HashSet<>();
   private final Set<Account.Id> extraCC = new HashSet<>();
   private final Set<Address> extraCCByEmail = new HashSet<>();
+  private final Set<Account.Id> removedReviewers = new HashSet<>();
+  private final Set<Address> removedByEmailReviewers = new HashSet<>();
 
   protected NewChangeSender(EmailArguments args, ChangeData changeData) {
     super(args, "newchange", changeData);
@@ -52,10 +54,17 @@
     extraCCByEmail.addAll(cc);
   }
 
+  public void addRemovedReviewers(Collection<Account.Id> removed) {
+    removedReviewers.addAll(removed);
+  }
+
+  public void addRemovedByEmailReviewers(Collection<Address> removed) {
+    removedByEmailReviewers.addAll(removed);
+  }
+
   @Override
   protected void init() throws EmailException {
     super.init();
-
     String threadId = getChangeMessageThreadId();
     setHeader("References", threadId);
 
@@ -71,6 +80,8 @@
       case OWNER_REVIEWERS:
         reviewers.stream().forEach(r -> add(RecipientType.TO, r, true));
         addByEmail(RecipientType.TO, reviewersByEmail, true);
+        removedReviewers.stream().forEach(r -> add(RecipientType.TO, r, true));
+        addByEmail(RecipientType.TO, removedByEmailReviewers, true);
         break;
     }
 
@@ -96,10 +107,25 @@
     return names;
   }
 
+  public List<String> getRemovedReviewerNames() {
+    if (removedReviewers.isEmpty() && removedByEmailReviewers.isEmpty()) {
+      return null;
+    }
+    List<String> names = new ArrayList<>();
+    for (Account.Id id : removedReviewers) {
+      names.add(getNameFor(id));
+    }
+    for (Address address : removedByEmailReviewers) {
+      names.add(address.name());
+    }
+    return names;
+  }
+
   @Override
   protected void setupSoyContext() {
     super.setupSoyContext();
     soyContext.put("ownerName", getNameFor(change.getOwner()));
     soyContextEmailData.put("reviewerNames", getReviewerNames());
+    soyContextEmailData.put("removedReviewerNames", getRemovedReviewerNames());
   }
 }
diff --git a/java/com/google/gerrit/server/restapi/change/DeleteReviewer.java b/java/com/google/gerrit/server/restapi/change/DeleteReviewer.java
index 3e4a483..db8e9de 100644
--- a/java/com/google/gerrit/server/restapi/change/DeleteReviewer.java
+++ b/java/com/google/gerrit/server/restapi/change/DeleteReviewer.java
@@ -64,7 +64,7 @@
       if (rsrc.isByEmail()) {
         op = deleteReviewerByEmailOpFactory.create(rsrc.getReviewerByEmail());
       } else {
-        op = deleteReviewerOpFactory.create(rsrc.getReviewerUser().state(), input);
+        op = deleteReviewerOpFactory.create(rsrc.getReviewerUser().getAccount(), input);
       }
       bu.addOp(rsrc.getChange().getId(), op);
       bu.execute();
diff --git a/java/com/google/gerrit/server/restapi/change/PostReview.java b/java/com/google/gerrit/server/restapi/change/PostReview.java
index b5f2ab1..8c1e655 100644
--- a/java/com/google/gerrit/server/restapi/change/PostReview.java
+++ b/java/com/google/gerrit/server/restapi/change/PostReview.java
@@ -16,6 +16,7 @@
 
 import static com.google.common.base.MoreObjects.firstNonNull;
 import static com.google.common.collect.ImmutableList.toImmutableList;
+import static com.google.common.collect.ImmutableSet.toImmutableSet;
 import static com.google.gerrit.entities.Patch.PATCHSET_LEVEL;
 import static com.google.gerrit.server.notedb.ReviewerStateInternal.REVIEWER;
 import static com.google.gerrit.server.permissions.LabelPermission.ForUser.ON_BEHALF_OF;
@@ -91,13 +92,13 @@
 import com.google.gerrit.server.PublishCommentUtil;
 import com.google.gerrit.server.ReviewerSet;
 import com.google.gerrit.server.account.AccountResolver;
-import com.google.gerrit.server.change.AddReviewersOp.Result;
 import com.google.gerrit.server.change.ChangeResource;
 import com.google.gerrit.server.change.EmailReviewComments;
 import com.google.gerrit.server.change.ModifyReviewersEmail;
 import com.google.gerrit.server.change.NotifyResolver;
 import com.google.gerrit.server.change.ReviewerModifier;
 import com.google.gerrit.server.change.ReviewerModifier.ReviewerModification;
+import com.google.gerrit.server.change.ReviewerOp.Result;
 import com.google.gerrit.server.change.RevisionResource;
 import com.google.gerrit.server.change.WorkInProgressOp;
 import com.google.gerrit.server.config.GerritServerConfig;
@@ -313,7 +314,7 @@
 
     try (BatchUpdate bu =
         updateFactory.create(revision.getChange().getProject(), revision.getUser(), ts)) {
-      Account.Id id = revision.getUser().getAccountId();
+      Account account = revision.getUser().asIdentifiedUser().getAccount();
       boolean ccOrReviewer = false;
       if (input.labels != null && !input.labels.isEmpty()) {
         ccOrReviewer = input.labels.values().stream().anyMatch(v -> v != 0);
@@ -326,7 +327,7 @@
         // Check if user was already CCed or reviewing prior to this review.
         ReviewerSet currentReviewers =
             approvalsUtil.getReviewers(revision.getChangeResource().getNotes());
-        ccOrReviewer = currentReviewers.all().contains(id);
+        ccOrReviewer = currentReviewers.all().contains(account.id());
         if (ccOrReviewer) {
           logger.atFine().log("calling user is already cc/reviewer on the change");
         }
@@ -339,7 +340,7 @@
       for (ReviewerModification reviewerResult : reviewerResults) {
         reviewerResult.op.suppressEmail(); // Send a single batch email below.
         bu.addOp(revision.getChange().getId(), reviewerResult.op);
-        if (!ccOrReviewer && reviewerResult.reviewers.contains(id)) {
+        if (!ccOrReviewer && reviewerResult.reviewers.contains(account)) {
           logger.atFine().log("calling user is explicitly added as reviewer or CC");
           ccOrReviewer = true;
         }
@@ -443,24 +444,39 @@
     try (TraceContext.TraceTimer ignored = newTimer("batchEmailReviewers")) {
       List<Account.Id> to = new ArrayList<>();
       List<Account.Id> cc = new ArrayList<>();
+      List<Account.Id> removed = new ArrayList<>();
       List<Address> toByEmail = new ArrayList<>();
       List<Address> ccByEmail = new ArrayList<>();
+      List<Address> removedByEmail = new ArrayList<>();
       for (ReviewerModification modification : reviewerModifications) {
         Result reviewAdditionResult = modification.op.getResult();
         if (modification.state() == ReviewerState.REVIEWER
             && (!reviewAdditionResult.addedReviewers().isEmpty()
                 || !reviewAdditionResult.addedReviewersByEmail().isEmpty())) {
-          to.addAll(modification.reviewers);
+          to.addAll(modification.reviewers.stream().map(Account::id).collect(toImmutableSet()));
           toByEmail.addAll(modification.reviewersByEmail);
         } else if (modification.state() == ReviewerState.CC
             && (!reviewAdditionResult.addedCCs().isEmpty()
                 || !reviewAdditionResult.addedCCsByEmail().isEmpty())) {
-          cc.addAll(modification.reviewers);
+          cc.addAll(modification.reviewers.stream().map(Account::id).collect(toImmutableSet()));
           ccByEmail.addAll(modification.reviewersByEmail);
+        } else if (modification.state() == ReviewerState.REMOVED
+            && (reviewAdditionResult.deletedReviewer().isPresent()
+                || reviewAdditionResult.deletedReviewerByEmail().isPresent())) {
+          reviewAdditionResult.deletedReviewer().ifPresent(d -> removed.add(d));
+          reviewAdditionResult.deletedReviewerByEmail().ifPresent(d -> removedByEmail.add(d));
         }
       }
       modifyReviewersEmail.emailReviewersAsync(
-          user.asIdentifiedUser(), change, to, cc, toByEmail, ccByEmail, notify);
+          user.asIdentifiedUser(),
+          change,
+          to,
+          cc,
+          removed,
+          toByEmail,
+          ccByEmail,
+          removedByEmail,
+          notify);
     }
   }
 
diff --git a/javatests/com/google/gerrit/acceptance/api/change/ChangeIT.java b/javatests/com/google/gerrit/acceptance/api/change/ChangeIT.java
index dee7861..b54e9cd 100644
--- a/javatests/com/google/gerrit/acceptance/api/change/ChangeIT.java
+++ b/javatests/com/google/gerrit/acceptance/api/change/ChangeIT.java
@@ -157,6 +157,7 @@
 import com.google.gerrit.index.query.PostFilterPredicate;
 import com.google.gerrit.server.ChangeMessagesUtil;
 import com.google.gerrit.server.StarredChangesUtil;
+import com.google.gerrit.server.change.ChangeMessages;
 import com.google.gerrit.server.change.ChangeResource;
 import com.google.gerrit.server.change.testing.TestChangeETagComputation;
 import com.google.gerrit.server.git.ChangeMessageModifier;
@@ -185,6 +186,7 @@
 import java.io.ByteArrayOutputStream;
 import java.io.IOException;
 import java.sql.Timestamp;
+import java.text.MessageFormat;
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Collection;
@@ -2113,6 +2115,46 @@
   }
 
   @Test
+  public void deleteGroupFromReviewersFails() throws Exception {
+    PushOneCommit.Result r = createChange();
+
+    // create a group named "kobe" with one user: lee
+    String myGroupUserEmail = "lee@example.com";
+    String myGroupUserFullname = "lee";
+    accountOperations
+        .newAccount()
+        .username("lee")
+        .preferredEmail(myGroupUserEmail)
+        .fullname(myGroupUserFullname)
+        .create();
+
+    String groupName = "kobe";
+    String testGroup = groupOperations.newGroup().name(groupName).create().get();
+    GroupApi groupApi = gApi.groups().id(testGroup);
+    groupApi.description("test group");
+    groupApi.addMembers(myGroupUserFullname);
+
+    // add the user as reviewer.
+    gApi.changes().id(r.getChangeId()).addReviewer(myGroupUserFullname);
+
+    // fail to remove that user via group.
+    ReviewResult reviewResult =
+        gApi.changes()
+            .id(r.getChangeId())
+            .current()
+            .review(ReviewInput.create().reviewer(testGroup, REMOVED, /* confirmed= */ true));
+
+    assertThat(reviewResult.error).isEqualTo("error adding reviewer");
+
+    ReviewerInput in = new ReviewerInput();
+    in.reviewer = testGroup;
+    in.state = REMOVED;
+    ReviewerResult reviewerResult = gApi.changes().id(r.getChangeId()).addReviewer(in);
+    assertThat(reviewerResult.error)
+        .isEqualTo(MessageFormat.format(ChangeMessages.get().groupRemovalIsNotAllowed, groupName));
+  }
+
+  @Test
   @UseClockStep
   public void addSelfAsReviewer() throws Exception {
     PushOneCommit.Result r = createChange();
diff --git a/javatests/com/google/gerrit/acceptance/api/change/PostReviewIT.java b/javatests/com/google/gerrit/acceptance/api/change/PostReviewIT.java
index 34679bd..b79be80 100644
--- a/javatests/com/google/gerrit/acceptance/api/change/PostReviewIT.java
+++ b/javatests/com/google/gerrit/acceptance/api/change/PostReviewIT.java
@@ -14,6 +14,7 @@
 
 package com.google.gerrit.acceptance.api.change;
 
+import static com.google.common.collect.ImmutableSet.toImmutableSet;
 import static com.google.common.truth.Truth.assertThat;
 import static com.google.gerrit.testing.GerritJUnit.assertThrows;
 import static java.util.stream.Collectors.toList;
@@ -47,6 +48,7 @@
 import com.google.gerrit.extensions.api.changes.ReviewInput.CommentInput;
 import com.google.gerrit.extensions.api.changes.ReviewInput.DraftHandling;
 import com.google.gerrit.extensions.api.changes.ReviewInput.RobotCommentInput;
+import com.google.gerrit.extensions.api.changes.ReviewResult;
 import com.google.gerrit.extensions.client.ReviewerState;
 import com.google.gerrit.extensions.client.Side;
 import com.google.gerrit.extensions.common.AccountInfo;
@@ -55,6 +57,7 @@
 import com.google.gerrit.extensions.config.FactoryModule;
 import com.google.gerrit.extensions.events.CommentAddedListener;
 import com.google.gerrit.extensions.restapi.BadRequestException;
+import com.google.gerrit.extensions.restapi.ResourceNotFoundException;
 import com.google.gerrit.extensions.restapi.RestApiException;
 import com.google.gerrit.extensions.validators.CommentForValidation;
 import com.google.gerrit.extensions.validators.CommentValidationContext;
@@ -66,6 +69,7 @@
 import com.google.gerrit.server.restapi.change.PostReview;
 import com.google.gerrit.server.rules.SubmitRule;
 import com.google.gerrit.server.update.CommentsRejectedException;
+import com.google.gerrit.testing.FakeEmailSender;
 import com.google.gerrit.testing.TestCommentHelper;
 import com.google.inject.Inject;
 import com.google.inject.Module;
@@ -74,6 +78,7 @@
 import java.util.List;
 import java.util.Map;
 import java.util.Optional;
+import java.util.regex.Pattern;
 import org.junit.Before;
 import org.junit.Test;
 import org.mockito.ArgumentCaptor;
@@ -693,6 +698,186 @@
     assertThat(testSubmitRule.count).isEqualTo(1);
   }
 
+  @Test
+  public void deletingReviewers() throws Exception {
+    PushOneCommit.Result r = createChange();
+
+    TestAccount user2 = accountCreator.user2();
+
+    // add user and user2
+    gApi.changes()
+        .id(r.getChangeId())
+        .current()
+        .review(ReviewInput.create().reviewer(user.email()).reviewer(user2.email()));
+
+    sender.clear();
+
+    // remove user and user2
+    ReviewResult reviewResult =
+        gApi.changes()
+            .id(r.getChangeId())
+            .current()
+            .review(
+                ReviewInput.create()
+                    .reviewer(user.email(), ReviewerState.REMOVED, /* confirmed= */ true)
+                    .reviewer(user2.email(), ReviewerState.REMOVED, /* confirmed= */ true));
+
+    assertThat(
+            reviewResult.reviewers.values().stream()
+                .map(a -> a.removed.name)
+                .collect(toImmutableSet()))
+        .containsExactly(user.fullName(), user2.fullName());
+
+    assertThat(gApi.changes().id(r.getChangeId()).reviewers()).isEmpty();
+
+    // Ensure only one batch email was sent for this operation
+    FakeEmailSender.Message message = Iterables.getOnlyElement(sender.getMessages());
+    assertThat(message.body())
+        .containsMatch(
+            Pattern.quote("removed ")
+                + "("
+                + Pattern.quote(String.format("%s, %s", user.fullName(), user2.fullName()))
+                + "|"
+                + Pattern.quote(String.format("%s, %s", user2.fullName(), user.fullName()))
+                + ")");
+    assertThat(message.htmlBody())
+        .containsMatch(
+            Pattern.quote("removed ")
+                + "("
+                + Pattern.quote(String.format("%s and %s", user.fullName(), user2.fullName()))
+                + "|"
+                + Pattern.quote(String.format("%s and %s", user2.fullName(), user.fullName()))
+                + ")");
+  }
+
+  @Test
+  public void addingAndDeletingReviewers() throws Exception {
+    PushOneCommit.Result r = createChange();
+
+    TestAccount user2 = accountCreator.user2();
+    TestAccount user3 = accountCreator.create("user3", "user3@email.com", "user3", "user3");
+    TestAccount user4 = accountCreator.create("user4", "user4@email.com", "user4", "user4");
+
+    // add user and user2
+    gApi.changes()
+        .id(r.getChangeId())
+        .current()
+        .review(ReviewInput.create().reviewer(user.email()).reviewer(user2.email()));
+
+    sender.clear();
+
+    // remove user and user2 while adding user3 and user4
+    ReviewResult reviewResult =
+        gApi.changes()
+            .id(r.getChangeId())
+            .current()
+            .review(
+                ReviewInput.create()
+                    .reviewer(user.email(), ReviewerState.REMOVED, /* confirmed= */ true)
+                    .reviewer(user2.email(), ReviewerState.REMOVED, /* confirmed= */ true)
+                    .reviewer(user3.email())
+                    .reviewer(user4.email()));
+
+    assertThat(
+            reviewResult.reviewers.values().stream()
+                .filter(a -> a.removed != null)
+                .map(a -> a.removed.name)
+                .collect(toImmutableSet()))
+        .containsExactly(user.fullName(), user2.fullName());
+    assertThat(
+            reviewResult.reviewers.values().stream()
+                .filter(a -> a.reviewers != null)
+                .map(a -> Iterables.getOnlyElement(a.reviewers).name)
+                .collect(toImmutableSet()))
+        .containsExactly(user3.fullName(), user4.fullName());
+
+    assertThat(
+            gApi.changes().id(r.getChangeId()).reviewers().stream()
+                .map(a -> a.name)
+                .collect(toImmutableSet()))
+        .containsExactly(user3.fullName(), user4.fullName());
+
+    // Ensure only one batch email was sent for this operation
+    FakeEmailSender.Message message = Iterables.getOnlyElement(sender.getMessages());
+    assertThat(message.body())
+        .containsMatch(
+            Pattern.quote("Hello ")
+                + "("
+                + Pattern.quote(String.format("%s, %s", user3.fullName(), user4.fullName()))
+                + "|"
+                + Pattern.quote(String.format("%s, %s", user4.fullName(), user3.fullName()))
+                + ")");
+    assertThat(message.htmlBody())
+        .containsMatch(
+            "("
+                + Pattern.quote(String.format("%s and %s", user3.fullName(), user4.fullName()))
+                + "|"
+                + Pattern.quote(String.format("%s and %s", user4.fullName(), user3.fullName()))
+                + ")"
+                + Pattern.quote(" to <strong>review</strong> this change"));
+
+    assertThat(message.body())
+        .containsMatch(
+            Pattern.quote("removed ")
+                + "("
+                + Pattern.quote(String.format("%s, %s", user.fullName(), user2.fullName()))
+                + "|"
+                + Pattern.quote(String.format("%s, %s", user2.fullName(), user.fullName()))
+                + ")");
+    assertThat(message.htmlBody())
+        .containsMatch(
+            Pattern.quote("removed ")
+                + "("
+                + Pattern.quote(String.format("%s and %s", user.fullName(), user2.fullName()))
+                + "|"
+                + Pattern.quote(String.format("%s and %s", user2.fullName(), user.fullName()))
+                + ")");
+  }
+
+  @Test
+  public void deletingNonExistingReviewerFails() throws Exception {
+    PushOneCommit.Result r = createChange();
+
+    ResourceNotFoundException resourceNotFoundException =
+        assertThrows(
+            ResourceNotFoundException.class,
+            () ->
+                gApi.changes()
+                    .id(r.getChangeId())
+                    .current()
+                    .review(
+                        ReviewInput.create()
+                            .reviewer(user.email(), ReviewerState.REMOVED, /* confirmed= */ true)));
+    assertThat(resourceNotFoundException)
+        .hasMessageThat()
+        .isEqualTo(
+            String.format(
+                "Reviewer %s doesn't exist in the change, hence can't delete it", user.fullName()));
+  }
+
+  @Test
+  public void addingAndDeletingSameReviewerFails() throws Exception {
+    PushOneCommit.Result r = createChange();
+
+    ResourceNotFoundException resourceNotFoundException =
+        assertThrows(
+            ResourceNotFoundException.class,
+            () ->
+                gApi.changes()
+                    .id(r.getChangeId())
+                    .current()
+                    .review(
+                        ReviewInput.create()
+                            .reviewer(user.email())
+                            .reviewer(user.email(), ReviewerState.REMOVED, true)));
+    assertThat(resourceNotFoundException)
+        .hasMessageThat()
+        .isEqualTo(
+            String.format(
+                "Reviewer %s doesn't exist in the change," + " hence can't delete it",
+                user.fullName()));
+  }
+
   private static class TestListener implements CommentAddedListener {
     public CommentAddedListener.Event lastCommentAddedEvent;
 
diff --git a/javatests/com/google/gerrit/acceptance/rest/change/ChangeReviewersIT.java b/javatests/com/google/gerrit/acceptance/rest/change/ChangeReviewersIT.java
index 41bedbc..db218b4 100644
--- a/javatests/com/google/gerrit/acceptance/rest/change/ChangeReviewersIT.java
+++ b/javatests/com/google/gerrit/acceptance/rest/change/ChangeReviewersIT.java
@@ -442,6 +442,7 @@
     assertThat(result.labels).isNull();
     assertThat(result.reviewers).isNotNull();
     assertThat(result.reviewers).hasSize(3);
+
     ReviewerResult reviewerResult = result.reviewers.get(largeGroup);
     assertThat(reviewerResult).isNotNull();
     assertThat(reviewerResult.confirm).isNull();
@@ -539,6 +540,7 @@
     ReviewResult result = review(r.getChangeId(), r.getCommit().name(), input);
     assertThat(result.reviewers).isNotNull();
     assertThat(result.reviewers).hasSize(1);
+
     ReviewerResult reviewerResult = result.reviewers.get(user.email());
     assertThat(reviewerResult).isNotNull();
     assertThat(reviewerResult.confirm).isNull();
@@ -564,6 +566,7 @@
     ReviewResult result = review(r.getChangeId(), r.getCommit().name(), input);
     assertThat(result.reviewers).isNotNull();
     assertThat(result.reviewers).hasSize(2);
+
     ReviewerResult reviewerResult = result.reviewers.get(group1);
     assertThat(reviewerResult.error).isNull();
     assertThat(reviewerResult.reviewers).hasSize(2);
diff --git a/resources/com/google/gerrit/server/change/ChangeMessages.properties b/resources/com/google/gerrit/server/change/ChangeMessages.properties
index 3763d8e..c78f5a3 100644
--- a/resources/com/google/gerrit/server/change/ChangeMessages.properties
+++ b/resources/com/google/gerrit/server/change/ChangeMessages.properties
@@ -7,6 +7,7 @@
 reviewerInvalid = {0} is not a valid user identifier
 reviewerNotFoundUserOrGroup = {0} does not identify a registered user or group
 
+groupRemovalIsNotAllowed = Groups can't be removed from reviewers, so can't remove {0}.
 groupIsNotAllowed = The group {0} cannot be added as reviewer.
 groupHasTooManyMembers = The group {0} has too many members to add them all as reviewers.
 groupManyMembersConfirmation = The group {0} has {1} members. Do you want to add them all as reviewers?
diff --git a/resources/com/google/gerrit/server/mail/NewChange.soy b/resources/com/google/gerrit/server/mail/NewChange.soy
index 0fe8835..aa2b946 100644
--- a/resources/com/google/gerrit/server/mail/NewChange.soy
+++ b/resources/com/google/gerrit/server/mail/NewChange.soy
@@ -23,23 +23,35 @@
 {template NewChange kind="text"}
   {@param change: ?}
   {@param email: ?}
+  {@param fromName: ?}
   {@param ownerName: ?}
   {@param patchSet: ?}
   {@param projectName: ?}
-  {if $email.reviewerNames}
-    Hello{sp}
-    {for $reviewerName in $email.reviewerNames}
-      {if not isFirst($reviewerName)},{sp}{/if}
-      {$reviewerName}
-    {/for},
+  {if $email.reviewerNames or $email.removedReviewerNames}
+   {if $email.reviewerNames}
+      Hello{sp}
+      {for $reviewerName in $email.reviewerNames}
+        {if not isFirst($reviewerName)},{sp}{/if}
+        {$reviewerName}
+      {/for},
 
-    {\n}
-    {\n}
+      {\n}
+      {\n}
 
-    I'd like you to do a code review.
-
+      I'd like you to do a code review.
+      {\n}
+    {/if}
+    {if $email.removedReviewerNames}
+      {$fromName} has removed{sp}
+      {for $reviewerName in $email.removedReviewerNames}
+        {if not isFirst($reviewerName)},{sp}{/if}
+        {$reviewerName}
+      {/for}{sp}
+      from this change.{sp}
+      {\n}
+    {/if}
     {if $email.changeUrl}
-      {sp}Please visit
+      Please visit
 
       {\n}
       {\n}
diff --git a/resources/com/google/gerrit/server/mail/NewChangeHtml.soy b/resources/com/google/gerrit/server/mail/NewChangeHtml.soy
index dbb3d8a..272c3ef 100644
--- a/resources/com/google/gerrit/server/mail/NewChangeHtml.soy
+++ b/resources/com/google/gerrit/server/mail/NewChangeHtml.soy
@@ -26,16 +26,35 @@
   {@param patchSet: ?}
   {@param projectName: ?}
   <p>
-    {if $email.reviewerNames}
-      {$fromName} would like{sp}
-      {for $reviewerName in $email.reviewerNames}
-        {if not isFirst($reviewerName)}
-          {if isLast($reviewerName)}{sp}and{else},{/if}{sp}
-        {/if}
-        {$reviewerName}
-      {/for}{sp}
-      to <strong>review</strong> this change
-      {if $fromName != $ownerName}{sp}authored by {$ownerName}{/if}.
+    {if $email.reviewerNames or $email.removedReviewerNames}
+      {if $email.reviewerNames}
+        {$fromName} would like{sp}
+        {for $reviewerName in $email.reviewerNames}
+          {if not isFirst($reviewerName)}
+            {if isLast($reviewerName)}{sp}and{else},{/if}{sp}
+          {/if}
+          {$reviewerName}
+        {/for}{sp}
+        to <strong>review</strong> this change
+        {if $fromName != $ownerName}{sp}authored by {$ownerName}{/if}.
+        {\n}
+      {/if}
+      {if $email.removedReviewerNames}
+        <p>
+          {$fromName}{sp}
+          <strong>
+            removed{sp}
+            {for $reviewerName in $email.removedReviewerNames}
+              {if not isFirst($reviewerName)}
+                {if isLast($reviewerName)}{sp}and{else},{/if}{sp}
+              {/if}
+              {$reviewerName}
+            {/for}
+          </strong>{sp}
+          from this change.
+        </p>
+        {\n}
+      {/if}
     {else}
       {$ownerName} has uploaded this change for <strong>review</strong>.
     {/if}