diff --git a/java/com/google/gerrit/server/AssigneeStatusUpdate.java b/java/com/google/gerrit/server/AssigneeStatusUpdate.java
new file mode 100644
index 0000000000..0da5edf981
--- /dev/null
+++ b/java/com/google/gerrit/server/AssigneeStatusUpdate.java
@@ -0,0 +1,21 @@
+package com.google.gerrit.server;
+
+import com.google.auto.value.AutoValue;
+import com.google.gerrit.entities.Account;
+import java.sql.Timestamp;
+import java.util.Optional;
+
+/** Change to an assignee's status. */
+@AutoValue
+public abstract class AssigneeStatusUpdate {
+  public static AssigneeStatusUpdate create(
+      Timestamp ts, Account.Id updatedBy, Optional<Account.Id> currentAssignee) {
+    return new AutoValue_AssigneeStatusUpdate(ts, updatedBy, currentAssignee);
+  }
+
+  public abstract Timestamp date();
+
+  public abstract Account.Id updatedBy();
+
+  public abstract Optional<Account.Id> currentAssignee();
+}
diff --git a/java/com/google/gerrit/server/notedb/ChangeNotes.java b/java/com/google/gerrit/server/notedb/ChangeNotes.java
index 384eebcb4e..8cf00461dc 100644
--- a/java/com/google/gerrit/server/notedb/ChangeNotes.java
+++ b/java/com/google/gerrit/server/notedb/ChangeNotes.java
@@ -16,6 +16,7 @@ package com.google.gerrit.server.notedb;
 
 import static com.google.common.base.Preconditions.checkArgument;
 import static com.google.common.base.Preconditions.checkState;
+import static com.google.common.collect.ImmutableSet.toImmutableSet;
 import static com.google.gerrit.entities.RefNames.changeMetaRef;
 import static java.util.Comparator.comparing;
 import static java.util.Objects.requireNonNull;
@@ -29,6 +30,7 @@ import com.google.common.collect.ImmutableSet;
 import com.google.common.collect.ImmutableSortedMap;
 import com.google.common.collect.ImmutableSortedSet;
 import com.google.common.collect.ListMultimap;
+import com.google.common.collect.Lists;
 import com.google.common.collect.MultimapBuilder;
 import com.google.common.collect.Multimaps;
 import com.google.common.collect.Ordering;
@@ -48,6 +50,7 @@ import com.google.gerrit.entities.Project;
 import com.google.gerrit.entities.RefNames;
 import com.google.gerrit.entities.RobotComment;
 import com.google.gerrit.exceptions.StorageException;
+import com.google.gerrit.server.AssigneeStatusUpdate;
 import com.google.gerrit.server.ReviewerByEmailSet;
 import com.google.gerrit.server.ReviewerSet;
 import com.google.gerrit.server.ReviewerStatusUpdate;
@@ -366,9 +369,24 @@ public class ChangeNotes extends AbstractChangeNotes<ChangeNotes> {
     return state.reviewerUpdates();
   }
 
-  /** @return an ImmutableSet of Account.Ids of all users that have been assigned to this change. */
+  /**
+   * @return an ImmutableSet of Account.Ids of all users that have been assigned to this change. The
+   *     order of the set is the order in which they were assigned.
+   */
   public ImmutableSet<Account.Id> getPastAssignees() {
-    return state.pastAssignees();
+    return Lists.reverse(state.assigneeUpdates()).stream()
+        .map(AssigneeStatusUpdate::currentAssignee)
+        .filter(Optional::isPresent)
+        .map(Optional::get)
+        .collect(toImmutableSet());
+  }
+
+  /**
+   * @return an ImmutableList of AssigneeStatusUpdate of all the updates to the assignee field to
+   *     this change. The order of the list is from most recent updates to least recent.
+   */
+  public ImmutableList<AssigneeStatusUpdate> getAssigneeUpdates() {
+    return state.assigneeUpdates();
   }
 
   /** @return a ImmutableSet of all hashtags for this change sorted in alphabetical order. */
diff --git a/java/com/google/gerrit/server/notedb/ChangeNotesCache.java b/java/com/google/gerrit/server/notedb/ChangeNotesCache.java
index 03073d2fe2..8f5fefec59 100644
--- a/java/com/google/gerrit/server/notedb/ChangeNotesCache.java
+++ b/java/com/google/gerrit/server/notedb/ChangeNotesCache.java
@@ -61,7 +61,7 @@ public class ChangeNotesCache {
             .weigher(Weigher.class)
             .maximumWeight(10 << 20)
             .diskLimit(-1)
-            .version(1)
+            .version(2)
             .keySerializer(Key.Serializer.INSTANCE)
             .valueSerializer(ChangeNotesState.Serializer.INSTANCE);
       }
@@ -148,11 +148,8 @@ public class ChangeNotesCache {
           + str(state.columns().originalSubject())
           + P
           + str(state.columns().submissionId())
-          + ptr(state.columns().assignee(), K) // assignee
           + P // status
           + P
-          + set(state.pastAssignees(), K)
-          + P
           + set(state.hashtags(), str(10))
           + P
           + list(state.patchSets(), patchSet())
@@ -169,6 +166,8 @@ public class ChangeNotesCache {
           + P
           + list(state.reviewerUpdates(), 4 * O + K + K + P)
           + P
+          + list(state.assigneeUpdates(), 4 * O + K + K)
+          + P
           + list(state.submitRecords(), P + list(2, str(4) + P + K) + P)
           + P
           + list(state.changeMessages(), changeMessage())
diff --git a/java/com/google/gerrit/server/notedb/ChangeNotesParser.java b/java/com/google/gerrit/server/notedb/ChangeNotesParser.java
index c4c227ee88..a3c47470a5 100644
--- a/java/com/google/gerrit/server/notedb/ChangeNotesParser.java
+++ b/java/com/google/gerrit/server/notedb/ChangeNotesParser.java
@@ -67,6 +67,7 @@ import com.google.gerrit.entities.PatchSetApproval;
 import com.google.gerrit.entities.RefNames;
 import com.google.gerrit.mail.Address;
 import com.google.gerrit.metrics.Timer1;
+import com.google.gerrit.server.AssigneeStatusUpdate;
 import com.google.gerrit.server.ReviewerByEmailSet;
 import com.google.gerrit.server.ReviewerSet;
 import com.google.gerrit.server.ReviewerStatusUpdate;
@@ -115,6 +116,7 @@ class ChangeNotesParser {
   private final Table<Address, ReviewerStateInternal, Timestamp> reviewersByEmail;
   private final List<Account.Id> allPastReviewers;
   private final List<ReviewerStatusUpdate> reviewerUpdates;
+  private final List<AssigneeStatusUpdate> assigneeUpdates;
   private final List<SubmitRecord> submitRecords;
   private final ListMultimap<ObjectId, Comment> comments;
   private final Map<PatchSet.Id, PatchSet.Builder> patchSets;
@@ -129,8 +131,6 @@ class ChangeNotesParser {
   private String branch;
   private Change.Status status;
   private String topic;
-  private Optional<Account.Id> assignee;
-  private List<Account.Id> pastAssignees;
   private Set<String> hashtags;
   private Timestamp createdOn;
   private Timestamp lastUpdatedOn;
@@ -172,6 +172,7 @@ class ChangeNotesParser {
     pendingReviewersByEmail = ReviewerByEmailSet.empty();
     allPastReviewers = new ArrayList<>();
     reviewerUpdates = new ArrayList<>();
+    assigneeUpdates = new ArrayList<>();
     submitRecords = Lists.newArrayListWithExpectedSize(1);
     allChangeMessages = new ArrayList<>();
     comments = MultimapBuilder.hashKeys().arrayListValues().build();
@@ -231,9 +232,7 @@ class ChangeNotesParser {
         topic,
         originalSubject,
         submissionId,
-        assignee != null ? assignee.orElse(null) : null,
         status,
-        Sets.newLinkedHashSet(Lists.reverse(pastAssignees)),
         firstNonNull(hashtags, ImmutableSet.of()),
         buildPatchSets(),
         buildApprovals(),
@@ -243,6 +242,7 @@ class ChangeNotesParser {
         pendingReviewersByEmail,
         allPastReviewers,
         buildReviewerUpdates(),
+        assigneeUpdates,
         submitRecords,
         buildAllMessages(),
         comments,
@@ -361,7 +361,7 @@ class ChangeNotesParser {
     }
 
     parseHashtags(commit);
-    parseAssignee(commit);
+    parseAssigneeUpdates(ts, commit);
 
     if (submissionId == null) {
       submissionId = parseSubmissionId(commit);
@@ -566,10 +566,8 @@ class ChangeNotesParser {
     }
   }
 
-  private void parseAssignee(ChangeNotesCommit commit) throws ConfigInvalidException {
-    if (pastAssignees == null) {
-      pastAssignees = Lists.newArrayList();
-    }
+  private void parseAssigneeUpdates(Timestamp ts, ChangeNotesCommit commit)
+      throws ConfigInvalidException {
     String assigneeValue = parseOneFooter(commit, FOOTER_ASSIGNEE);
     if (assigneeValue != null) {
       Optional<Account.Id> parsedAssignee;
@@ -580,12 +578,7 @@ class ChangeNotesParser {
         PersonIdent ident = RawParseUtils.parsePersonIdent(assigneeValue);
         parsedAssignee = Optional.ofNullable(legacyChangeNoteRead.parseIdent(ident, id));
       }
-      if (assignee == null) {
-        assignee = parsedAssignee;
-      }
-      if (parsedAssignee.isPresent()) {
-        pastAssignees.add(parsedAssignee.get());
-      }
+      assigneeUpdates.add(AssigneeStatusUpdate.create(ts, ownerId, parsedAssignee));
     }
   }
 
diff --git a/java/com/google/gerrit/server/notedb/ChangeNotesState.java b/java/com/google/gerrit/server/notedb/ChangeNotesState.java
index 53965086c0..896cca3ba4 100644
--- a/java/com/google/gerrit/server/notedb/ChangeNotesState.java
+++ b/java/com/google/gerrit/server/notedb/ChangeNotesState.java
@@ -18,7 +18,6 @@ import static com.google.common.base.Preconditions.checkArgument;
 import static com.google.common.base.Preconditions.checkState;
 import static com.google.common.collect.ImmutableList.toImmutableList;
 import static com.google.common.collect.ImmutableListMultimap.toImmutableListMultimap;
-import static com.google.common.collect.ImmutableSet.toImmutableSet;
 import static java.util.Objects.requireNonNull;
 
 import com.google.auto.value.AutoValue;
@@ -50,10 +49,12 @@ import com.google.gerrit.entities.converter.ProtoConverter;
 import com.google.gerrit.json.OutputFormat;
 import com.google.gerrit.mail.Address;
 import com.google.gerrit.proto.Protos;
+import com.google.gerrit.server.AssigneeStatusUpdate;
 import com.google.gerrit.server.ReviewerByEmailSet;
 import com.google.gerrit.server.ReviewerSet;
 import com.google.gerrit.server.ReviewerStatusUpdate;
 import com.google.gerrit.server.cache.proto.Cache.ChangeNotesStateProto;
+import com.google.gerrit.server.cache.proto.Cache.ChangeNotesStateProto.AssigneeStatusUpdateProto;
 import com.google.gerrit.server.cache.proto.Cache.ChangeNotesStateProto.ChangeColumnsProto;
 import com.google.gerrit.server.cache.proto.Cache.ChangeNotesStateProto.ReviewerByEmailSetEntryProto;
 import com.google.gerrit.server.cache.proto.Cache.ChangeNotesStateProto.ReviewerSetEntryProto;
@@ -67,6 +68,7 @@ import com.google.protobuf.MessageLite;
 import java.sql.Timestamp;
 import java.util.List;
 import java.util.Map;
+import java.util.Optional;
 import java.util.Set;
 import org.eclipse.jgit.lib.ObjectId;
 
@@ -103,9 +105,7 @@ public abstract class ChangeNotesState {
       @Nullable String topic,
       @Nullable String originalSubject,
       @Nullable String submissionId,
-      @Nullable Account.Id assignee,
       @Nullable Change.Status status,
-      Set<Account.Id> pastAssignees,
       Set<String> hashtags,
       Map<PatchSet.Id, PatchSet> patchSets,
       ListMultimap<PatchSet.Id, PatchSetApproval> approvals,
@@ -115,6 +115,7 @@ public abstract class ChangeNotesState {
       ReviewerByEmailSet pendingReviewersByEmail,
       List<Account.Id> allPastReviewers,
       List<ReviewerStatusUpdate> reviewerUpdates,
+      List<AssigneeStatusUpdate> assigneeUpdates,
       List<SubmitRecord> submitRecords,
       List<ChangeMessage> changeMessages,
       ListMultimap<ObjectId, Comment> publishedComments,
@@ -147,13 +148,11 @@ public abstract class ChangeNotesState {
                 .topic(topic)
                 .originalSubject(originalSubject)
                 .submissionId(submissionId)
-                .assignee(assignee)
                 .isPrivate(isPrivate)
                 .workInProgress(workInProgress)
                 .reviewStarted(reviewStarted)
                 .revertOf(revertOf)
                 .build())
-        .pastAssignees(pastAssignees)
         .hashtags(hashtags)
         .serverId(serverId)
         .patchSets(patchSets.entrySet())
@@ -164,6 +163,7 @@ public abstract class ChangeNotesState {
         .pendingReviewersByEmail(pendingReviewersByEmail)
         .allPastReviewers(allPastReviewers)
         .reviewerUpdates(reviewerUpdates)
+        .assigneeUpdates(assigneeUpdates)
         .submitRecords(submitRecords)
         .changeMessages(changeMessages)
         .publishedComments(publishedComments)
@@ -211,9 +211,6 @@ public abstract class ChangeNotesState {
     @Nullable
     abstract String submissionId();
 
-    @Nullable
-    abstract Account.Id assignee();
-
     abstract boolean isPrivate();
 
     abstract boolean workInProgress();
@@ -247,8 +244,6 @@ public abstract class ChangeNotesState {
 
       abstract Builder submissionId(@Nullable String submissionId);
 
-      abstract Builder assignee(@Nullable Account.Id assignee);
-
       abstract Builder status(@Nullable Change.Status status);
 
       abstract Builder isPrivate(boolean isPrivate);
@@ -274,8 +269,6 @@ public abstract class ChangeNotesState {
   abstract ChangeColumns columns();
 
   // Other related to this Change.
-  abstract ImmutableSet<Account.Id> pastAssignees();
-
   abstract ImmutableSet<String> hashtags();
 
   @Nullable
@@ -297,6 +290,8 @@ public abstract class ChangeNotesState {
 
   abstract ImmutableList<ReviewerStatusUpdate> reviewerUpdates();
 
+  abstract ImmutableList<AssigneeStatusUpdate> assigneeUpdates();
+
   abstract ImmutableList<SubmitRecord> submitRecords();
 
   abstract ImmutableList<ChangeMessage> changeMessages();
@@ -339,7 +334,9 @@ public abstract class ChangeNotesState {
     change.setTopic(Strings.emptyToNull(c.topic()));
     change.setLastUpdatedOn(c.lastUpdatedOn());
     change.setSubmissionId(c.submissionId());
-    change.setAssignee(c.assignee());
+    if (!assigneeUpdates().isEmpty()) {
+      change.setAssignee(assigneeUpdates().get(0).currentAssignee().orElse(null));
+    }
     change.setPrivate(c.isPrivate());
     change.setWorkInProgress(c.workInProgress());
     change.setReviewStarted(c.reviewStarted());
@@ -359,7 +356,6 @@ public abstract class ChangeNotesState {
     static Builder empty(Change.Id changeId) {
       return new AutoValue_ChangeNotesState.Builder()
           .changeId(changeId)
-          .pastAssignees(ImmutableSet.of())
           .hashtags(ImmutableSet.of())
           .patchSets(ImmutableList.of())
           .approvals(ImmutableList.of())
@@ -369,6 +365,7 @@ public abstract class ChangeNotesState {
           .pendingReviewersByEmail(ReviewerByEmailSet.empty())
           .allPastReviewers(ImmutableList.of())
           .reviewerUpdates(ImmutableList.of())
+          .assigneeUpdates(ImmutableList.of())
           .submitRecords(ImmutableList.of())
           .changeMessages(ImmutableList.of())
           .publishedComments(ImmutableListMultimap.of())
@@ -383,8 +380,6 @@ public abstract class ChangeNotesState {
 
     abstract Builder serverId(String serverId);
 
-    abstract Builder pastAssignees(Set<Account.Id> pastAssignees);
-
     abstract Builder hashtags(Iterable<String> hashtags);
 
     abstract Builder patchSets(Iterable<Map.Entry<PatchSet.Id, PatchSet>> patchSets);
@@ -403,6 +398,8 @@ public abstract class ChangeNotesState {
 
     abstract Builder reviewerUpdates(List<ReviewerStatusUpdate> reviewerUpdates);
 
+    abstract Builder assigneeUpdates(List<AssigneeStatusUpdate> assigneeUpdates);
+
     abstract Builder submitRecords(List<SubmitRecord> submitRecords);
 
     abstract Builder changeMessages(List<ChangeMessage> changeMessages);
@@ -438,7 +435,6 @@ public abstract class ChangeNotesState {
         b.setServerId(object.serverId());
         b.setHasServerId(true);
       }
-      object.pastAssignees().forEach(a -> b.addPastAssignee(a.get()));
       object.hashtags().forEach(b::addHashtag);
       object
           .patchSets()
@@ -469,6 +465,7 @@ public abstract class ChangeNotesState {
 
       object.allPastReviewers().forEach(a -> b.addPastReviewer(a.get()));
       object.reviewerUpdates().forEach(u -> b.addReviewerUpdate(toReviewerStatusUpdateProto(u)));
+      object.assigneeUpdates().forEach(u -> b.addAssigneeUpdate(toAssigneeStatusUpdateProto(u)));
       object
           .submitRecords()
           .forEach(r -> b.addSubmitRecord(GSON.toJson(new StoredSubmitRecord(r))));
@@ -508,9 +505,6 @@ public abstract class ChangeNotesState {
       if (cols.submissionId() != null) {
         b.setSubmissionId(cols.submissionId()).setHasSubmissionId(true);
       }
-      if (cols.assignee() != null) {
-        b.setAssignee(cols.assignee().get()).setHasAssignee(true);
-      }
       if (cols.status() != null) {
         b.setStatus(STATUS_CONVERTER.reverse().convert(cols.status())).setHasStatus(true);
       }
@@ -550,6 +544,17 @@ public abstract class ChangeNotesState {
           .build();
     }
 
+    private static AssigneeStatusUpdateProto toAssigneeStatusUpdateProto(AssigneeStatusUpdate u) {
+      AssigneeStatusUpdateProto.Builder builder =
+          AssigneeStatusUpdateProto.newBuilder()
+              .setDate(u.date().getTime())
+              .setUpdatedBy(u.updatedBy().get())
+              .setHasCurrentAssignee(u.currentAssignee().isPresent());
+
+      u.currentAssignee().ifPresent(assignee -> builder.setCurrentAssignee(assignee.get()));
+      return builder.build();
+    }
+
     @Override
     public ChangeNotesState deserialize(byte[] in) {
       ChangeNotesStateProto proto = Protos.parseUnchecked(ChangeNotesStateProto.parser(), in);
@@ -561,8 +566,6 @@ public abstract class ChangeNotesState {
               .changeId(changeId)
               .columns(toChangeColumns(changeId, proto.getColumns()))
               .serverId(proto.getHasServerId() ? proto.getServerId() : null)
-              .pastAssignees(
-                  proto.getPastAssigneeList().stream().map(Account::id).collect(toImmutableSet()))
               .hashtags(proto.getHashtagList())
               .patchSets(
                   proto.getPatchSetList().stream()
@@ -581,6 +584,7 @@ public abstract class ChangeNotesState {
               .allPastReviewers(
                   proto.getPastReviewerList().stream().map(Account::id).collect(toImmutableList()))
               .reviewerUpdates(toReviewerStatusUpdateList(proto.getReviewerUpdateList()))
+              .assigneeUpdates(toAssigneeStatusUpdateList(proto.getAssigneeUpdateList()))
               .submitRecords(
                   proto.getSubmitRecordList().stream()
                       .map(r -> GSON.fromJson(r, StoredSubmitRecord.class).toSubmitRecord())
@@ -624,9 +628,6 @@ public abstract class ChangeNotesState {
       if (proto.getHasSubmissionId()) {
         b.submissionId(proto.getSubmissionId());
       }
-      if (proto.getHasAssignee()) {
-        b.assignee(Account.id(proto.getAssignee()));
-      }
       if (proto.getHasStatus()) {
         b.status(STATUS_CONVERTER.convert(proto.getStatus()));
       }
@@ -677,5 +678,20 @@ public abstract class ChangeNotesState {
       }
       return b.build();
     }
+
+    private static ImmutableList<AssigneeStatusUpdate> toAssigneeStatusUpdateList(
+        List<AssigneeStatusUpdateProto> protos) {
+      ImmutableList.Builder<AssigneeStatusUpdate> b = ImmutableList.builder();
+      for (AssigneeStatusUpdateProto proto : protos) {
+        b.add(
+            AssigneeStatusUpdate.create(
+                new Timestamp(proto.getDate()),
+                Account.id(proto.getUpdatedBy()),
+                proto.getHasCurrentAssignee()
+                    ? Optional.of(Account.id(proto.getCurrentAssignee()))
+                    : Optional.empty()));
+      }
+      return b.build();
+    }
   }
 }
diff --git a/javatests/com/google/gerrit/server/notedb/ChangeNotesParserTest.java b/javatests/com/google/gerrit/server/notedb/ChangeNotesParserTest.java
index ed79be62fa..7882518f9a 100644
--- a/javatests/com/google/gerrit/server/notedb/ChangeNotesParserTest.java
+++ b/javatests/com/google/gerrit/server/notedb/ChangeNotesParserTest.java
@@ -213,6 +213,26 @@ public class ChangeNotesParserTest extends AbstractChangeNotesTest {
     assertParseFails("Update change\n\nPatch-set: 1\nReviewer: 1@gerrit\n");
   }
 
+  @Test
+  public void parseAssignee() throws Exception {
+    assertParseSucceeds(
+        "Update change\n"
+            + "\n"
+            + "Branch: refs/heads/master\n"
+            + "Change-id: I577fb248e474018276351785930358ec0450e9f7\n"
+            + "Patch-set: 1\n"
+            + "Assignee: Change Owner <1@gerrit>\n"
+            + "Subject: This is a test change\n");
+    assertParseSucceeds(
+        "Update change\n"
+            + "\n"
+            + "Branch: refs/heads/master\n"
+            + "Change-id: I577fb248e474018276351785930358ec0450e9f7\n"
+            + "Patch-set: 2\n"
+            + "Assignee:\n"
+            + "Subject: This is a test change\n");
+  }
+
   @Test
   public void parseTopic() throws Exception {
     assertParseSucceeds(
diff --git a/javatests/com/google/gerrit/server/notedb/ChangeNotesStateTest.java b/javatests/com/google/gerrit/server/notedb/ChangeNotesStateTest.java
index d381e99e96..0d7f2bd171 100644
--- a/javatests/com/google/gerrit/server/notedb/ChangeNotesStateTest.java
+++ b/javatests/com/google/gerrit/server/notedb/ChangeNotesStateTest.java
@@ -38,10 +38,12 @@ import com.google.gerrit.entities.converter.ChangeMessageProtoConverter;
 import com.google.gerrit.entities.converter.PatchSetApprovalProtoConverter;
 import com.google.gerrit.entities.converter.PatchSetProtoConverter;
 import com.google.gerrit.mail.Address;
+import com.google.gerrit.server.AssigneeStatusUpdate;
 import com.google.gerrit.server.ReviewerByEmailSet;
 import com.google.gerrit.server.ReviewerSet;
 import com.google.gerrit.server.ReviewerStatusUpdate;
 import com.google.gerrit.server.cache.proto.Cache.ChangeNotesStateProto;
+import com.google.gerrit.server.cache.proto.Cache.ChangeNotesStateProto.AssigneeStatusUpdateProto;
 import com.google.gerrit.server.cache.proto.Cache.ChangeNotesStateProto.ChangeColumnsProto;
 import com.google.gerrit.server.cache.proto.Cache.ChangeNotesStateProto.ReviewerByEmailSetEntryProto;
 import com.google.gerrit.server.cache.proto.Cache.ChangeNotesStateProto.ReviewerSetEntryProto;
@@ -241,17 +243,6 @@ public class ChangeNotesStateTest {
             .build());
   }
 
-  @Test
-  public void serializeAssignee() throws Exception {
-    assertRoundTrip(
-        newBuilder().columns(cols.toBuilder().assignee(Account.id(2000)).build()).build(),
-        ChangeNotesStateProto.newBuilder()
-            .setMetaId(SHA_BYTES)
-            .setChangeId(ID.get())
-            .setColumns(colsProto.toBuilder().setAssignee(2000).setHasAssignee(true))
-            .build());
-  }
-
   @Test
   public void serializeStatus() throws Exception {
     assertRoundTrip(
@@ -307,19 +298,6 @@ public class ChangeNotesStateTest {
             .build());
   }
 
-  @Test
-  public void serializePastAssignees() throws Exception {
-    assertRoundTrip(
-        newBuilder().pastAssignees(ImmutableSet.of(Account.id(2002), Account.id(2001))).build(),
-        ChangeNotesStateProto.newBuilder()
-            .setMetaId(SHA_BYTES)
-            .setChangeId(ID.get())
-            .setColumns(colsProto)
-            .addPastAssignee(2002)
-            .addPastAssignee(2001)
-            .build());
-  }
-
   @Test
   public void serializeHashtags() throws Exception {
     assertRoundTrip(
@@ -610,6 +588,35 @@ public class ChangeNotesStateTest {
             .build());
   }
 
+  @Test
+  public void serializeAssigneeUpdates() throws Exception {
+    assertRoundTrip(
+        newBuilder()
+            .assigneeUpdates(
+                ImmutableList.of(
+                    AssigneeStatusUpdate.create(
+                        new Timestamp(1212L), Account.id(1000), Optional.of(Account.id(2001))),
+                    AssigneeStatusUpdate.create(
+                        new Timestamp(3434L), Account.id(1000), Optional.empty())))
+            .build(),
+        ChangeNotesStateProto.newBuilder()
+            .setMetaId(SHA_BYTES)
+            .setChangeId(ID.get())
+            .setColumns(colsProto)
+            .addAssigneeUpdate(
+                AssigneeStatusUpdateProto.newBuilder()
+                    .setDate(1212L)
+                    .setUpdatedBy(1000)
+                    .setCurrentAssignee(2001)
+                    .setHasCurrentAssignee(true))
+            .addAssigneeUpdate(
+                AssigneeStatusUpdateProto.newBuilder()
+                    .setDate(3434L)
+                    .setUpdatedBy(1000)
+                    .setHasCurrentAssignee(false))
+            .build());
+  }
+
   @Test
   public void serializeSubmitRecords() throws Exception {
     SubmitRecord sr1 = new SubmitRecord();
@@ -721,7 +728,6 @@ public class ChangeNotesStateTest {
                 .put("changeId", Change.Id.class)
                 .put("serverId", String.class)
                 .put("columns", ChangeColumns.class)
-                .put("pastAssignees", new TypeLiteral<ImmutableSet<Account.Id>>() {}.getType())
                 .put("hashtags", new TypeLiteral<ImmutableSet<String>>() {}.getType())
                 .put(
                     "patchSets",
@@ -738,6 +744,9 @@ public class ChangeNotesStateTest {
                 .put(
                     "reviewerUpdates",
                     new TypeLiteral<ImmutableList<ReviewerStatusUpdate>>() {}.getType())
+                .put(
+                    "assigneeUpdates",
+                    new TypeLiteral<ImmutableList<AssigneeStatusUpdate>>() {}.getType())
                 .put("submitRecords", new TypeLiteral<ImmutableList<SubmitRecord>>() {}.getType())
                 .put("changeMessages", new TypeLiteral<ImmutableList<ChangeMessage>>() {}.getType())
                 .put(
@@ -762,7 +771,6 @@ public class ChangeNotesStateTest {
                 .put("topic", String.class)
                 .put("originalSubject", String.class)
                 .put("submissionId", String.class)
-                .put("assignee", Account.Id.class)
                 .put("status", Change.Status.class)
                 .put("isPrivate", boolean.class)
                 .put("workInProgress", boolean.class)
@@ -843,6 +851,19 @@ public class ChangeNotesStateTest {
                 "state", ReviewerStateInternal.class));
   }
 
+  @Test
+  public void assigneeStatusUpdateMethods() throws Exception {
+    assertThatSerializedClass(AssigneeStatusUpdate.class)
+        .hasAutoValueMethods(
+            ImmutableMap.of(
+                "date",
+                Timestamp.class,
+                "updatedBy",
+                Account.Id.class,
+                "currentAssignee",
+                new TypeLiteral<Optional<Account.Id>>() {}.getType()));
+  }
+
   @Test
   public void submitRecordFields() throws Exception {
     assertThatSerializedClass(SubmitRecord.class)
diff --git a/javatests/com/google/gerrit/server/notedb/ChangeNotesTest.java b/javatests/com/google/gerrit/server/notedb/ChangeNotesTest.java
index 2ed145ee0d..a4c395c11b 100644
--- a/javatests/com/google/gerrit/server/notedb/ChangeNotesTest.java
+++ b/javatests/com/google/gerrit/server/notedb/ChangeNotesTest.java
@@ -48,6 +48,7 @@ import com.google.gerrit.entities.PatchSet;
 import com.google.gerrit.entities.PatchSetApproval;
 import com.google.gerrit.exceptions.StorageException;
 import com.google.gerrit.mail.Address;
+import com.google.gerrit.server.AssigneeStatusUpdate;
 import com.google.gerrit.server.CurrentUser;
 import com.google.gerrit.server.IdentifiedUser;
 import com.google.gerrit.server.ReviewerSet;
@@ -744,6 +745,35 @@ public class ChangeNotesTest extends AbstractChangeNotesTest {
     assertThat(notes.getPastAssignees()).hasSize(2);
   }
 
+  @Test
+  public void assigneeStatusUpdateChangeNotes() throws Exception {
+    Change c = newChange();
+    ChangeUpdate update = newUpdate(c, otherUser);
+    update.setAssignee(otherUserId);
+    update.commit();
+
+    update = newUpdate(c, changeOwner);
+    update.removeAssignee();
+    update.commit();
+
+    update = newUpdate(c, changeOwner);
+    update.setAssignee(changeOwner.getAccountId());
+    update.commit();
+
+    update = newUpdate(c, changeOwner);
+    update.setAssignee(otherUserId);
+    update.commit();
+
+    ChangeNotes notes = newNotes(c);
+    ImmutableList<AssigneeStatusUpdate> statusUpdates = notes.getAssigneeUpdates();
+    assertThat(statusUpdates).hasSize(4);
+    assertThat(statusUpdates.get(3).updatedBy()).isEqualTo(otherUserId);
+    assertThat(statusUpdates.get(3).currentAssignee()).hasValue(otherUserId);
+    assertThat(statusUpdates.get(2).currentAssignee()).isEmpty();
+    assertThat(statusUpdates.get(1).currentAssignee()).hasValue(changeOwner.getAccountId());
+    assertThat(statusUpdates.get(0).currentAssignee()).hasValue(otherUserId);
+  }
+
   @Test
   public void hashtagCommit() throws Exception {
     Change c = newChange();
diff --git a/proto/cache.proto b/proto/cache.proto
index 2a0764098c..10e0216cf1 100644
--- a/proto/cache.proto
+++ b/proto/cache.proto
@@ -75,7 +75,7 @@ message ChangeNotesKeyProto {
 // Instead, we just take the tedious yet simple approach of having a "has_foo"
 // field for each nullable field "foo", indicating whether or not foo is null.
 //
-// Next ID: 20
+// Next ID: 23
 message ChangeNotesStateProto {
   // Effectively required, even though the corresponding ChangeNotesState field
   // is optional, since the field is only absent when NoteDb is disabled, in
@@ -110,8 +110,8 @@ message ChangeNotesStateProto {
     string submission_id = 13;
     bool has_submission_id = 14;
 
-    int32 assignee = 15;
-    bool has_assignee = 16;
+    reserved 15;  // assignee
+    reserved 16;  // has_assignee
 
     string status = 17;
     bool has_status = 18;
@@ -130,7 +130,7 @@ message ChangeNotesStateProto {
   // which case attempting to use the ChangeNotesCache is programmer error.
   ChangeColumnsProto columns = 3;
 
-  repeated int32 past_assignee = 4;
+  reserved  4; // past_assignee
 
   repeated string hashtag = 5;
 
@@ -189,6 +189,14 @@ message ChangeNotesStateProto {
 
   string server_id = 20;
   bool has_server_id = 21;
+
+  message AssigneeStatusUpdateProto {
+    int64 date = 1;
+    int32 updated_by = 2;
+    int32 current_assignee = 3;
+    bool has_current_assignee = 4;
+  }
+  repeated AssigneeStatusUpdateProto assignee_update = 22;
 }