diff --git a/lib/pleroma/web/activity_pub/activity_pub.ex b/lib/pleroma/web/activity_pub/activity_pub.ex
index 491ad3705..48eba36fd 100644
--- a/lib/pleroma/web/activity_pub/activity_pub.ex
+++ b/lib/pleroma/web/activity_pub/activity_pub.ex
@@ -199,6 +199,29 @@ def delete(%Object{data: %{"id" => id, "actor" => actor}} = object, local \\ tru
     end
   end
 
+  def block(blocker, blocked, local \\ true) do
+    follow_activity = fetch_latest_follow(blocker, blocked)
+
+    if follow_activity do
+      unfollow(blocker, blocked, local)
+    end
+
+    with block_data <- make_block_data(blocker, blocked),
+         {:ok, activity} <- insert(block_data, local),
+         :ok <- maybe_federate(activity) do
+      {:ok, activity}
+    end
+  end
+
+  def unblock(blocker, blocked, local \\ true) do
+    with %Activity{} = block_activity <- fetch_latest_block(blocker, blocked),
+         unblock_data <- make_unblock_data(blocker, blocked, block_activity),
+         {:ok, activity} <- insert(unblock_data, local),
+         :ok <- maybe_federate(activity) do
+      {:ok, activity}
+    end
+  end
+
   def fetch_activities_for_context(context, opts \\ %{}) do
     public = ["https://www.w3.org/ns/activitystreams#Public"]
 
diff --git a/lib/pleroma/web/activity_pub/transmogrifier.ex b/lib/pleroma/web/activity_pub/transmogrifier.ex
index 0bec8c4dd..cc0033a5f 100644
--- a/lib/pleroma/web/activity_pub/transmogrifier.ex
+++ b/lib/pleroma/web/activity_pub/transmogrifier.ex
@@ -259,6 +259,24 @@ def handle_incoming(
     end
   end
 
+  def handle_incoming(%{"type" => "Undo", "object" => object_id} = data) do
+    object = Object.get_by_ap_id(object_id).data
+    data = Map.put(data, "object", object)
+
+    handle_incoming(data)
+  end
+
+  def handle_incoming(%{"type" => "Block", "object" => blocked, "actor" => blocker, "id" => id} = data) do
+    with %User{local: true} = blocked = User.get_cached_by_ap_id(blocked),
+         %User{} = blocker = User.get_or_fetch_by_ap_id(blocker),
+         {:ok, activity} <- ActivityPub.block(blocker, blocked, false) do
+      User.unfollow(follower, followed)
+      User.block(blocker, blocked.ap_id)
+      {:ok, activity}
+    else
+      e -> :error
+    end
+  end
   # TODO
   # Accept
   # Undo for non-Announce
diff --git a/lib/pleroma/web/activity_pub/utils.ex b/lib/pleroma/web/activity_pub/utils.ex
index f98545336..c29fc6b07 100644
--- a/lib/pleroma/web/activity_pub/utils.ex
+++ b/lib/pleroma/web/activity_pub/utils.ex
@@ -322,6 +322,41 @@ def make_unfollow_data(follower, followed, follow_activity) do
     }
   end
 
+  #### Block-related helpers
+  def fetch_latest_block(%User{ap_id: blocker_id}, %User{ap_id: blocked_id}) do
+    query =
+      from(
+        activity in Activity,
+        where:
+          fragment(
+            "? @> ?",
+            activity.data,
+            ^%{type: "Block", actor: blocker_id, object: blocked_id}
+          ),
+        order_by: [desc: :id],
+        limit: 1
+      )
+
+    Repo.one(query)
+  end
+
+  def make_block_data(blocker, blocked) do
+    %{
+      "type" => "Block",
+      "actor" => blocker.ap_id,
+      "to" => [blocked.ap_id],
+      "object" => blocked.ap_id
+    }
+  end
+
+  def make_unblock_data(blocker, blocked, block_activity) do
+    %{
+      "type" => "Undo",
+      "actor" => blocker.ap_id,
+      "to" => [blocked.ap_id],
+      "object" => block_activity.data
+    }
+  end
   #### Create-related helpers
 
   def make_create_data(params, additional) do