diff --git a/src/Room.c b/src/Room.c
index 34a4029..6766773 100644
--- a/src/Room.c
+++ b/src/Room.c
@@ -1815,32 +1815,44 @@ RoomAddEventV1(Room *room, PduV1 pdu)
     /* TODO: Store DAG relationships, somehow.
      * Also keep track of PDU depth. */
 
-    if (StrEquals(pdu.type, "m.room.member"))
+    pdu_json = PduV1ToJson(&pdu);
     {
-        CommonID *id = UserIdParse(pdu.state_key, NULL);
-        User *user   = UserLock(room->db, id->local);
-        char *membership = JsonValueAsString(
-            HashMapGet(pdu.content, "membership")
-        );
+        CommonID *sid= UserIdParse(pdu.sender, NULL);
+        User *suser  = UserLock(room->db, sid->local);
+        if (StrEquals(pdu.type, "m.room.member"))
+        {
+            CommonID *id = UserIdParse(pdu.state_key, NULL);
+            User *user   = UserLock(room->db, id->local);
+            char *membership = JsonValueAsString(
+                HashMapGet(pdu.content, "membership")
+            );
 
-        if (StrEquals(membership, "join") && user)
-        {
-            UserAddJoin(user, room->id);
-        }
-        else if (StrEquals(membership, "invite") && user)
-        {
-            UserAddInvite(user, room->id);
-        }
-        else if ((StrEquals(membership, "leave") && user) ||
-                StrEquals(membership, "ban"))
-        {
-            UserRemoveInvite(user, room->id);
-            UserRemoveJoin(user, room->id);
+            if (StrEquals(membership, "join") && user)
+            {
+                UserAddJoin(user, room->id);
+                UserPushJoinSync(user, room->id);
+            }
+            else if (StrEquals(membership, "invite") && user)
+            {
+                UserAddInvite(user, room->id);
+                UserPushInviteSync(user, room->id);
+            }
+            else if ((StrEquals(membership, "leave") && user) ||
+                    StrEquals(membership, "ban"))
+            {
+                UserRemoveInvite(user, room->id);
+                UserRemoveJoin(user, room->id);
+            }
+
+            UserIdFree(id);
+            UserUnlock(user);
         }
 
-        UserIdFree(id);
-        UserUnlock(user);
+        UserPushEvent(suser, pdu_json);
+        UserIdFree(sid);
+        UserUnlock(suser);
     }
+    JsonFree(pdu_json);
 
     return true;
 }
diff --git a/src/User.c b/src/User.c
index 4bdab9f..8d38ea3 100644
--- a/src/User.c
+++ b/src/User.c
@@ -22,6 +22,7 @@
  * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
  * SOFTWARE.
  */
+#include <Cytoplasm/Db.h>
 #include <User.h>
 #include <Cytoplasm/Util.h>
 #include <Cytoplasm/Memory.h>
@@ -1114,3 +1115,149 @@ UserFreeList(Array *arr)
 
     ArrayFree(arr);
 }
+char *
+UserInitSyncDiff(User *user)
+{
+    char *nextBatch;
+    DbRef *syncRef;
+    HashMap *data;
+
+    if (!user)
+    {
+        return NULL;
+    }
+
+    nextBatch = StrRandom(16);
+    syncRef = DbCreate(user->db, 4, "users", user->name, "sync", nextBatch);
+    if (!syncRef)
+    {
+        Free(nextBatch);
+        return NULL;
+    }
+
+    data = DbJson(syncRef);
+
+    HashMapSet(data, "nextBatch", JsonValueString(nextBatch));
+    HashMapSet(data, "invites", JsonValueArray(ArrayCreate()));
+    HashMapSet(data, "leaves", JsonValueArray(ArrayCreate()));
+    HashMapSet(data, "joins", JsonValueObject(HashMapCreate()));
+
+    DbUnlock(user->db, syncRef);
+
+    return nextBatch;
+}
+
+void
+UserPushInviteSync(User *user, char *roomId)
+{
+    DbRef *syncRef;
+    HashMap *data;
+    Array *entries;
+    Array *invites;
+    size_t i;
+    if (!user || !roomId)
+    {
+        return;
+    }
+
+    entries = DbList(user->db, 3, "users", user->name, "sync");
+    for (i = 0; i < ArraySize(entries); i++)
+    {
+        char *entry = ArrayGet(entries, i);
+        syncRef = DbLock(user->db, 4, "users", user->name, "sync", entry);
+        data = DbJson(syncRef);
+        invites = JsonValueAsArray(HashMapGet(data, "invites"));
+
+        ArrayAdd(invites, JsonValueString(roomId));
+
+        DbUnlock(user->db, syncRef);
+    }
+    DbListFree(entries);
+}
+void
+UserPushJoinSync(User *user, char *roomId)
+{
+    DbRef *syncRef;
+    HashMap *data;
+    Array *entries;
+    HashMap *join;
+    size_t i;
+    if (!user || !roomId)
+    {
+        return;
+    }
+
+    entries = DbList(user->db, 3, "users", user->name, "sync");
+    for (i = 0; i < ArraySize(entries); i++)
+    {
+        char *entry = ArrayGet(entries, i);
+        HashMap *joinEntry;
+        syncRef = DbLock(user->db, 4, "users", user->name, "sync", entry);
+        data = DbJson(syncRef);
+        join = JsonValueAsObject(HashMapGet(data, "joins"));
+
+        /* TODO */
+        joinEntry = HashMapCreate();
+        HashMapSet(joinEntry, "timeline", JsonValueArray(ArrayCreate()));
+
+        if (!HashMapGet(join, roomId))
+        {
+            JsonFree(HashMapSet(join, roomId, JsonValueObject(joinEntry)));
+        }
+        else
+        {
+            JsonFree(joinEntry);
+        }
+
+        DbUnlock(user->db, syncRef);
+    }
+    DbListFree(entries);
+}
+
+void
+UserPushEvent(User *user, HashMap *event)
+{
+    DbRef *syncRef;
+    HashMap *data;
+    Array *entries;
+    HashMap *join;
+    size_t i;
+    char *roomId, *eventId;
+    if (!user || !event)
+    {
+        return;
+    }
+
+    roomId = JsonValueAsString(HashMapGet(event, "room_id"));
+    eventId = JsonValueAsString(HashMapGet(event, "event_id"));
+
+    UserPushJoinSync(user, roomId);
+
+    entries = DbList(user->db, 3, "users", user->name, "sync");
+    for (i = 0; i < ArraySize(entries); i++)
+    {
+        char *entry = ArrayGet(entries, i);
+        HashMap *joinEntry;
+        Array *timeline;
+        syncRef = DbLock(user->db, 4, "users", user->name, "sync", entry);
+        data = DbJson(syncRef);
+        join = JsonValueAsObject(HashMapGet(data, "joins"));
+
+        joinEntry = JsonValueAsObject(HashMapGet(join, roomId));
+        timeline = JsonValueAsArray(HashMapGet(joinEntry, "timeline"));
+
+        ArrayAdd(timeline, JsonValueString(eventId));
+
+        DbUnlock(user->db, syncRef);
+    }
+    DbListFree(entries);
+}
+void
+UserDropSync(User *user, char *batch)
+{
+    if (!user || !batch)
+    {
+        return;
+    }
+    DbDelete(user->db, 4, "users", user->name, "sync", batch);
+}
diff --git a/src/include/User.h b/src/include/User.h
index 632f892..f67794a 100644
--- a/src/include/User.h
+++ b/src/include/User.h
@@ -314,6 +314,7 @@ extern HashMap * UserGetTransaction(User *, char *, char *);
  */
 extern void UserSetTransaction(User *, char *, char *, HashMap *);
 
+
 /**
  * Puts a room (indexed by room ID) in a user's invite list.
  */
@@ -361,4 +362,30 @@ extern void UserFreeList(Array *);
  */
 extern void UserIdFree(CommonID *);
 
+/** 
+ * Initialises a sync diff table, and returns a next_batch parameter, 
+ * which is stored on the heap.
+ */
+extern char * UserInitSyncDiff(User *);
+
+/**
+ * Pushes an invite onto all sync diff tables.
+ */
+extern void UserPushInviteSync(User *, char *);
+
+/**
+ * Pushes a join onto all sync diff tables.
+ */
+extern void UserPushJoinSync(User *, char *);
+
+/**
+ * Pushes an event (ID) into every diff table of a user.
+ */
+extern void UserPushEvent(User *, HashMap *);
+
+/**
+ * Drops a sync diff, denoted by it's previous batch ID, if it 
+ * exists.
+ */
+extern void UserDropSync(User *, char *);
 #endif                             /* TELODENDRIA_USER_H */