diff --git a/hooks-its/src/main/java/com/googlesource/gerrit/plugins/hooks/workflow/Condition.java b/hooks-its/src/main/java/com/googlesource/gerrit/plugins/hooks/workflow/Condition.java
index 47aae91..61aa365 100644
--- a/hooks-its/src/main/java/com/googlesource/gerrit/plugins/hooks/workflow/Condition.java
+++ b/hooks-its/src/main/java/com/googlesource/gerrit/plugins/hooks/workflow/Condition.java
@@ -14,27 +14,34 @@
 
 package com.googlesource.gerrit.plugins.hooks.workflow;
 
-import java.util.Arrays;
 import java.util.Collections;
+import java.util.List;
 import java.util.Set;
 
 import javax.annotation.Nullable;
 
+import com.google.common.collect.Lists;
 import com.google.common.collect.Sets;
 import com.google.inject.Inject;
 import com.google.inject.assistedinject.Assisted;
 
 /**
  * A condition as used in {@link Rule}, as precondition to {@link Action}s.
- *
- * A condition consists of a key and an associated set of values. A condition
- * is said to match a set of properties, is this set contains at least one
- * property that matches the rules key and whose value matches at least one
- * of the rule's value.
+ * <p>
+ * A condition consists of a key and an associated set of values.
+ * <p>
+ * For positive conditions (see constructor), the condition is said to match a
+ * set of properties, if this set contains at least one property that matches
+ * the rules key and whose value matches at least one of the rule's value.
+ * <p>
+ * For negated conditions (see constructor), the condition is said to match a
+ * set of properties, if this set does not contain any property that matches
+ * the rules key and whose value matches at least one of the rule's value.
  */
 public class Condition {
   private final String key;
   private final Set<String> values;
+  private final boolean negated;
 
   public interface Factory {
     Condition create(@Assisted("key") String key,
@@ -44,19 +51,29 @@
   /**
    * Constructs a condition.
    * @param key The key to use for values.
-   * @param values A comma separated list of values to associate to the key.
+   * @param values A comma separated list of values to associate to the key. If
+   *    the first value is not "!", it's a positive condition. If the first
+   *    value is "!", the "!" is removed from the values and the condition is
+   *    considered a negated condition.
    */
   @Inject
   public Condition(@Assisted("key") String key,
       @Nullable @Assisted("values") String values) {
     this.key = key;
     Set<String> modifyableValues;
+    boolean modifyableNegated = false;
     if (values == null) {
       modifyableValues = Collections.emptySet();
     } else {
-      modifyableValues = Sets.newHashSet(Arrays.asList(values.split(",")));
+      List<String> valueList = Lists.newArrayList(values.split(","));
+      if (!valueList.isEmpty() && "!".equals(valueList.get(0))) {
+        modifyableNegated = true;
+        valueList.remove(0);
+      }
+      modifyableValues = Sets.newHashSet(valueList);
     }
     this.values = Collections.unmodifiableSet(modifyableValues);
+    this.negated = modifyableNegated;
   }
 
   public String getKey() {
@@ -67,8 +84,11 @@
    * Checks whether or not the Condition matches the given set of properties
    *
    * @param properties The set of properties to match against.
-   * @return True iff properties contains at least one property that matches
-   *    the rules key and whose value matches at least one of the rule's value.
+   * @return For positive conditions, true iff properties contains at least
+   *    one property that matches the rules key and whose value matches at
+   *    least one of the rule's value. For negated conditions, true iff
+   *    properties does not contain any property that matches the rules key
+   *    and whose value matches at least one of the rule's value.
    */
   public boolean isMetBy(Iterable<Property> properties) {
     for (Property property : properties) {
@@ -76,11 +96,11 @@
       if ((key == null && propertyKey == null)
           || (key != null && key.equals(propertyKey))) {
         if (values.contains(property.getValue())) {
-          return true;
+          return !negated;
         }
       }
     }
-    return false;
+    return negated;
   }
 
   @Override
diff --git a/hooks-its/src/main/resources/Documentation/config.md b/hooks-its/src/main/resources/Documentation/config.md
index 2593171..a4ccfd1 100644
--- a/hooks-its/src/main/resources/Documentation/config.md
+++ b/hooks-its/src/main/resources/Documentation/config.md
@@ -94,9 +94,22 @@
 ----
 name = value1, value2, ..., valueN
 ----
-and match if the event comes with a property 'name' having 'value1',
-or 'value2', or ..., or 'valueN'.
+and (if 'value1' is not +!+) match if the event comes with a property
+'name' having 'value1', or 'value2', or ..., or 'valueN'. So for
+example to match events that come with an 'association' property
+having 'subject', or 'footer-Bug', the following condition can be
+used:
+----
+association = subject,footer-Bug
+----
 
+If 'value1' is +!+, the conditon matches if the event does not come
+with a property 'name' having 'value2', or ..., or 'valueN'. So for
+example to match events that do not come with a 'status' property
+having 'DRAFT', the following condition can be used:
+----
+status = !,DRAFT
+----
 
 [[event-properties]]
 Event Properties
diff --git a/hooks-its/src/test/java/com/googlesource/gerrit/plugins/hooks/workflow/ConditionTest.java b/hooks-its/src/test/java/com/googlesource/gerrit/plugins/hooks/workflow/ConditionTest.java
index 857f9e8..886ab40 100644
--- a/hooks-its/src/test/java/com/googlesource/gerrit/plugins/hooks/workflow/ConditionTest.java
+++ b/hooks-its/src/test/java/com/googlesource/gerrit/plugins/hooks/workflow/ConditionTest.java
@@ -172,6 +172,146 @@
     assertTrue("isMetBy gave false", condition.isMetBy(properties));
   }
 
+  public void testNegatedIsMetByEmpty() {
+    Condition condition = createCondition("testKey", "!,testValue");
+
+    Collection<Property> properties = Collections.emptySet();
+
+    replayMocks();
+
+    assertTrue("isMetBy gave false", condition.isMetBy(properties));
+  }
+
+  public void testNegatedIsMetByMismatchedKey() {
+    Condition condition = createCondition("testKey", "!,testValue");
+
+    Property property1 = createMock(Property.class);
+    expect(property1.getKey()).andReturn("otherKey").anyTimes();
+    expect(property1.getValue()).andReturn("testValue").anyTimes();
+
+    Collection<Property> properties = Lists.newArrayListWithCapacity(1);
+    properties.add(property1);
+
+    replayMocks();
+
+    assertTrue("isMetBy gave false", condition.isMetBy(properties));
+  }
+
+  public void testNegatedIsMetByMaMismatchedValue() {
+    Condition condition = createCondition("testKey", "!,testValue");
+
+    Property property1 = createMock(Property.class);
+    expect(property1.getKey()).andReturn("testKey").anyTimes();
+    expect(property1.getValue()).andReturn("otherValue").anyTimes();
+
+    Collection<Property> properties = Lists.newArrayListWithCapacity(1);
+    properties.add(property1);
+
+    replayMocks();
+
+    assertTrue("isMetBy gave false", condition.isMetBy(properties));
+  }
+
+  public void testNegatedIsMetByOredNoMatch() {
+    Condition condition = createCondition("testKey", "!,value1,value2,value3");
+
+    Property property1 = createMock(Property.class);
+    expect(property1.getKey()).andReturn("testKey").anyTimes();
+    expect(property1.getValue()).andReturn("otherValue").anyTimes();
+
+    Collection<Property> properties = Lists.newArrayListWithCapacity(1);
+    properties.add(property1);
+
+    replayMocks();
+
+    assertTrue("isMetBy gave false", condition.isMetBy(properties));
+  }
+
+  public void testNegatedIsMetByOredSingleMatch() {
+    Condition condition = createCondition("testKey", "!,value1,value2,value3");
+
+    Property property1 = createMock(Property.class);
+    expect(property1.getKey()).andReturn("testKey").anyTimes();
+    expect(property1.getValue()).andReturn("value1").anyTimes();
+
+    Collection<Property> properties = Lists.newArrayListWithCapacity(1);
+    properties.add(property1);
+
+    replayMocks();
+
+    assertFalse("isMetBy gave true", condition.isMetBy(properties));
+  }
+
+  public void testNegatedIsMetByOredMultiple() {
+    Condition condition = createCondition("testKey", "!,value1,value2,value3");
+
+    Property property1 = createMock(Property.class);
+    expect(property1.getKey()).andReturn("testKey").anyTimes();
+    expect(property1.getValue()).andReturn("value1").anyTimes();
+
+    Property property2 = createMock(Property.class);
+    expect(property2.getKey()).andReturn("testKey").anyTimes();
+    expect(property2.getValue()).andReturn("value3").anyTimes();
+
+    Collection<Property> properties = Lists.newArrayListWithCapacity(2);
+    properties.add(property1);
+    properties.add(property2);
+
+    replayMocks();
+
+    assertFalse("isMetBy gave true", condition.isMetBy(properties));
+  }
+
+  public void testNegatedIsMetByOredAll() {
+    Condition condition = createCondition("testKey", "!,value1,value2,value3");
+
+    Property property1 = createMock(Property.class);
+    expect(property1.getKey()).andReturn("testKey").anyTimes();
+    expect(property1.getValue()).andReturn("value1").anyTimes();
+
+    Property property2 = createMock(Property.class);
+    expect(property2.getKey()).andReturn("testKey").anyTimes();
+    expect(property2.getValue()).andReturn("value2").anyTimes();
+
+    Property property3 = createMock(Property.class);
+    expect(property3.getKey()).andReturn("testKey").anyTimes();
+    expect(property3.getValue()).andReturn("value3").anyTimes();
+
+    Collection<Property> properties = Lists.newArrayListWithCapacity(1);
+    properties.add(property1);
+    properties.add(property2);
+    properties.add(property3);
+
+    replayMocks();
+
+    assertFalse("isMetBy gave true", condition.isMetBy(properties));
+  }
+
+  public void testNegatedIsMetByOredOvershoot() {
+    Condition condition = createCondition("testKey", "!,value1,value2,value3");
+
+    Property property1 = createMock(Property.class);
+    expect(property1.getKey()).andReturn("testKey").anyTimes();
+    expect(property1.getValue()).andReturn("otherValue1").anyTimes();
+
+    Property property2 = createMock(Property.class);
+    expect(property2.getKey()).andReturn("testKey").anyTimes();
+    expect(property2.getValue()).andReturn("value2").anyTimes();
+
+    Property property3 = createMock(Property.class);
+    expect(property3.getKey()).andReturn("testKey").anyTimes();
+    expect(property3.getValue()).andReturn("otherValue3").anyTimes();
+
+    Collection<Property> properties = Lists.newArrayListWithCapacity(3);
+    properties.add(property1);
+    properties.add(property2);
+    properties.add(property3);
+
+    replayMocks();
+
+    assertFalse("isMetBy gave true", condition.isMetBy(properties));
+  }
+
   private Condition createCondition(String key, String value) {
     Condition.Factory factory = injector.getInstance(Condition.Factory.class);
     return factory.create(key, value);