diff --git a/lib/phoenix/channel.ex b/lib/phoenix/channel.ex
index 165eba5bbb..a106746e81 100644
--- a/lib/phoenix/channel.ex
+++ b/lib/phoenix/channel.ex
@@ -48,7 +48,7 @@ defmodule Phoenix.Channel do
   After a client has successfully joined a channel, incoming events from the
   client are routed through the channel's `handle_in/3` callbacks. Within these
   callbacks, you can perform any action. Typically you'll either foward a
-  message out to all listeners with `Phoenix.Channel.broadcast/3`, or reply
+  message out to all listeners with `Phoenix.Channel.broadcast!/3`, or reply
   directly to the socket with `Phoenix.Channel.reply/3`.
   Incoming callbacks must return the `socket` to maintain ephemeral state.
 
@@ -56,7 +56,7 @@ defmodule Phoenix.Channel do
   and broadcasting the message to all topic subscribers for this socket.
 
       def handle_in("new:msg", %{"uid" => uid, "body" => body}, socket) do
-        broadcast socket, "new:msg", %{uid: uid, body: body}
+        broadcast! socket, "new:msg", %{uid: uid, body: body}
         {:ok, socket}
       end
 
@@ -75,10 +75,10 @@ defmodule Phoenix.Channel do
   subscribers' `handle_out/3` callback is triggered where the event can be
   relayed as is, or customized on a socket by socket basis to append extra
   information, or conditionally filter the message from being delivered.
-  *Note*: `broadcast/3` and `reply/3` both return `{:ok, socket}`.
+  *Note*: `broadcast/3`, `broadcast!/3` and `reply/3` both return `{:ok, socket}`.
 
       def handle_in("new:msg", %{"uid" => uid, "body" => body}, socket) do
-        broadcast socket, "new:msg", %{uid: uid, body: body}
+        broadcast! socket, "new:msg", %{uid: uid, body: body}
       end
 
       # for every socket subscribing on this topic, append an `is_editable`
@@ -156,13 +156,22 @@ defmodule Phoenix.Channel do
       def broadcast_from(socket = %Socket{}, event, msg) do
         Phoenix.Channel.broadcast_from(@pubsub_server, socket, event, msg)
       end
+      def broadcast_from!(socket = %Socket{}, event, msg) do
+        Phoenix.Channel.broadcast_from!(@pubsub_server, socket, event, msg)
+      end
       def broadcast_from(from, topic, event, msg) when is_map(msg) do
         Phoenix.Channel.broadcast_from(@pubsub_server, from, topic, event, msg)
       end
+      def broadcast_from!(from, topic, event, msg) when is_map(msg) do
+        Phoenix.Channel.broadcast_from!(@pubsub_server, from, topic, event, msg)
+      end
 
       def broadcast(topic_or_socket, event, msg) do
         Phoenix.Channel.broadcast(@pubsub_server, topic_or_socket, event, msg)
       end
+      def broadcast!(topic_or_socket, event, msg) do
+        Phoenix.Channel.broadcast!(@pubsub_server, topic_or_socket, event, msg)
+      end
 
       defoverridable leave: 2, handle_out: 3
     end
@@ -182,12 +191,23 @@ defmodule Phoenix.Channel do
   def broadcast(server, topic, event, message) when is_binary(topic) do
     broadcast_from server, :none, topic, event, message
   end
-
   def broadcast(server, socket = %Socket{}, event, message) do
     broadcast_from server, :none, socket.topic, event, message
     {:ok, socket}
   end
 
+  @doc """
+  Same as `Phoenix.Channel.broadcast/4`, but
+  raises `Phoenix.PubSub.BroadcastError` if broadcast fails
+  """
+  def broadcast!(server, topic, event, message) when is_binary(topic) do
+    broadcast_from! server, :none, topic, event, message
+  end
+  def broadcast!(server, socket = %Socket{}, event, message) do
+    broadcast_from! server, :none, socket.topic, event, message
+    {:ok, socket}
+  end
+
   @doc """
   Broadcast event from pid, serializable as JSON to channel
   The broadcasting socket `from`, does not receive the published message.
@@ -212,6 +232,23 @@ defmodule Phoenix.Channel do
   end
   def broadcast_from(_, _, _, _, _), do: raise_invalid_message
 
+  @doc """
+  Same as `Phoenix.Channel.broadcast_from/4`, but
+  raises `Phoenix.PubSub.BroadcastError` if broadcast fails
+  """
+  def broadcast_from!(pubsub_server, socket = %Socket{}, event, message) do
+    broadcast_from!(pubsub_server, socket.pid, socket.topic, event, message)
+    {:ok, socket}
+  end
+  def broadcast_from!(pubsub_server, from, topic, event, message) when is_map(message) do
+    PubSub.broadcast_from! pubsub_server, from, topic, {:socket_broadcast, %Message{
+      topic: topic,
+      event: event,
+      payload: message
+    }}
+  end
+  def broadcast_from!(_, _, _, _, _), do: raise_invalid_message
+
   @doc """
   Sends Dict, JSON serializable message to socket
   """
diff --git a/lib/phoenix/pubsub.ex b/lib/phoenix/pubsub.ex
index 52f838b67b..01b9ff4a3d 100644
--- a/lib/phoenix/pubsub.ex
+++ b/lib/phoenix/pubsub.ex
@@ -1,10 +1,37 @@
 defmodule Phoenix.PubSub do
-  import GenServer, only: [call: 2]
 
   @moduledoc """
   Serves as a Notification and PubSub layer for broad use-cases. Used internally
   by Channels for pubsub broadcast.
 
+  ## PubSub Adapter Contract
+  PubSub adapters need to only respond to a few process-based messages to
+  integrate with Phoenix. PubSub functions send the following messages:
+
+    * `subscribe` -
+       sends:        `{:subscribe, pid, topic, link}`
+       respond with: `:ok | {:error, reason} {:perform, {m, f a}}`
+
+    * `unsubscribe` -
+       sends:        `{:unsubscribe, pid, topic}`
+       respond with: `:ok | {:error, reason} {:perform, {m, f a}}`
+
+    * `subscribers` -
+       respond with: `:ok | {:error, reason} {:perform, {m, f a}}`
+
+    * `broadcast` -
+       sends          `{:broadcast, :none, topic, message}`
+       respond with: `:ok | {:error, reason} {:perform, {m, f a}}`
+
+
+  ### Offloading work to clients via MFA response
+  The `Phoenix.PubSub` API allows any of its functions to handle a
+  response from the adapter matching `{:perform, {m, f a}}`. The PubSub
+  client will recursively invoke all MFA responses until a result is
+  return. This is useful for offloading work to clients without blocking
+  in your PubSub adapter. See `Phoenix.PubSub.PG2` for an example usage.
+
+
   ## Example
 
       iex> PubSub.subscribe(self, "user:123")
@@ -20,6 +47,13 @@ defmodule Phoenix.PubSub do
 
   """
 
+  defmodule BroadcastError do
+    defexception [:message]
+    def exception(msg) do
+      %BroadcastError{message: "Broadcast failed with #{inspect msg}"}
+    end
+  end
+
 
   @doc """
   Subscribes the pid to the pg2 group for the topic
@@ -55,15 +89,46 @@ defmodule Phoenix.PubSub do
   def broadcast(server, topic, message),
     do: call(server, {:broadcast, :none, topic, message})
 
+  @doc """
+  Broadcasts message on given topic
+  raises `Phoenix.PubSub.BroadcastError` if broadcast fails
+  """
+  def broadcast!(server, topic, message, broadcaster \\ __MODULE__) do
+    case broadcaster.broadcast(server, topic, message) do
+      :ok -> :ok
+      {:error, reason} -> raise BroadcastError, message: reason
+    end
+  end
+
   @doc """
   Broadcasts message to all but sender on given topic
   """
   def broadcast_from(server, from_pid, topic, message),
     do: call(server, {:broadcast, from_pid, topic, message})
 
+  @doc """
+  Broadcasts message to all but sender on given topic
+  raises `Phoenix.PubSub.BroadcastError` if broadcast fails
+  """
+  def broadcast_from!(server, from_pid, topic, message, broadcaster \\ __MODULE__) do
+    case broadcaster.broadcast_from(server, from_pid, topic, message) do
+      :ok -> :ok
+      {:error, reason} -> raise BroadcastError, message: reason
+    end
+  end
+
   @doc false
   # Returns list of all topics under local server, for debug and perf tuning
   def list(server_name) do
     GenServer.call(Module.concat(server_name, Local), :list)
   end
+
+  defp call(server, msg) do
+    GenServer.call(server, msg) |> perform
+  end
+
+  defp perform({:perform, {mod, func, args}}) do
+    apply(mod, func, args) |> perform
+  end
+  defp perform(result), do: result
 end
diff --git a/lib/phoenix/pubsub/pg2_server.ex b/lib/phoenix/pubsub/pg2_server.ex
index 782927d0a6..fd5c602e61 100644
--- a/lib/phoenix/pubsub/pg2_server.ex
+++ b/lib/phoenix/pubsub/pg2_server.ex
@@ -23,24 +23,29 @@ defmodule Phoenix.PubSub.PG2Server do
   end
 
   def handle_call({:subscribe, pid, topic, link}, _from, state) do
-    {:reply, GenServer.call(state.local_name, {:subscribe, pid, topic, link}), state}
+    response = {:perform, {GenServer, :call, [state.local_name, {:subscribe, pid, topic, link}]}}
+    {:reply, response, state}
   end
 
   def handle_call({:unsubscribe, pid, topic}, _from, state) do
-    {:reply, GenServer.call(state.local_name, {:unsubscribe, pid, topic}), state}
+    response = {:perform, {GenServer, :call, [state.local_name, {:unsubscribe, pid, topic}]}}
+    {:reply, response, state}
   end
 
   def handle_call({:broadcast, from_pid, topic, msg}, _from, state) do
     case :pg2.get_members(state.namespace) do
+      {:error, {:no_such_group, _}} ->
+        {:stop, :no_such_group, {:error, :no_such_group}, state}
+
       pids when is_list(pids) ->
         Enum.each(pids, &send(&1, {:forward_to_local, from_pid, topic, msg}))
+        {:reply, :ok, state}
     end
-
-    {:reply, :ok, state}
   end
 
   def handle_call({:subscribers, topic}, _from, state) do
-    {:reply, GenServer.call(state.local_name, {:subscribers, topic}), state}
+    response = {:perform, {GenServer, :call, [state.local_name, {:subscribers, topic}]}}
+    {:reply, response, state}
   end
 
   def handle_call(:stop, _from, state) do
diff --git a/lib/phoenix/pubsub/redis_server.ex b/lib/phoenix/pubsub/redis_server.ex
index c20e3e50a4..da898cd67b 100644
--- a/lib/phoenix/pubsub/redis_server.ex
+++ b/lib/phoenix/pubsub/redis_server.ex
@@ -21,6 +21,17 @@ defmodule Phoenix.PubSub.RedisServer do
     GenServer.start_link(__MODULE__, opts, name: Dict.fetch!(opts, :name))
   end
 
+  @doc """
+  Broadcasts message to redis. To be only called from {:perform, {m, f, a}}
+  response to clients
+  """
+  def broadcast(eredis_pid, namespace, redis_msg) do
+    case :eredis.q(eredis_pid, ["PUBLISH", namespace, redis_msg]) do
+      {:ok, _}         -> :ok
+      {:error, reason} -> {:error, reason}
+    end
+  end
+
   @doc """
   Initializes the server.
 
@@ -49,23 +60,24 @@ defmodule Phoenix.PubSub.RedisServer do
   end
 
   def handle_call({:subscribe, pid, topic, link}, _from, state) do
-    {:reply, GenServer.call(state.local_name, {:subscribe, pid, topic, link}), state}
+    response = {:perform, {GenServer, :call, [state.local_name, {:subscribe, pid, topic, link}]}}
+    {:reply, response, state}
   end
 
   def handle_call({:unsubscribe, pid, topic}, _from, state) do
-    {:reply, GenServer.call(state.local_name, {:unsubscribe, pid, topic}), state}
+    response = {:perform, {GenServer, :call, [state.local_name, {:unsubscribe, pid, topic}]}}
+    {:reply, response, state}
   end
 
   def handle_call({:subscribers, topic}, _from, state) do
-    {:reply, GenServer.call(state.local_name, {:subscribers, topic}), state}
+    response = {:perform, {GenServer, :call, [state.local_name, {:subscribers, topic}]}}
+    {:reply, response, state}
   end
 
   def handle_call({:broadcast, from_pid, topic, msg}, _from, state) do
     redis_msg = {@redis_msg_vsn, state.node_ref, from_pid, topic, msg}
-    case :eredis.q(state.eredis_pid, ["PUBLISH", state.namespace, redis_msg]) do
-      {:ok, _}         -> {:reply, :ok, state}
-      {:error, reason} -> {:reply, {:error, reason}, state}
-    end
+    resp = {:perform, {__MODULE__, :broadcast, [state.eredis_pid, state.namespace, redis_msg]}}
+    {:reply, resp, state}
   end
 
   @doc """
diff --git a/test/phoenix/channel_test.exs b/test/phoenix/channel_test.exs
index b0afbb26d2..e0ce5148d0 100644
--- a/test/phoenix/channel_test.exs
+++ b/test/phoenix/channel_test.exs
@@ -110,40 +110,54 @@ defmodule Phoenix.ChannelTest do
     assert PubSub.subscribers(:my_app_pub, "top:subtop") == HashSet.new
   end
 
-  test "#broadcast broadcasts global message on topic" do
+  test "#broadcast and #broadcast! broadcasts global message on topic" do
     socket = Socket.put_topic(new_socket, "top:subtop")
 
     assert Channel.broadcast(:my_app_pub, socket, "event", %{foo: "bar"})
+    assert Channel.broadcast!(:my_app_pub, socket, "event", %{foo: "bar"})
   end
 
-  test "#broadcast raises friendly error when message arg isn't a Map" do
+
+  test "#broadcast and #broadcast! raises friendly error when message arg isn't a Map" do
     message = "Message argument must be a map"
     assert_raise RuntimeError, message, fn ->
       Channel.broadcast(:my_app_pub, "topic:subtopic", "event", bar: "foo", foo: "bar")
     end
+    assert_raise RuntimeError, message, fn ->
+      Channel.broadcast!(:my_app_pub, "topic:subtopic", "event", bar: "foo", foo: "bar")
+    end
   end
 
-  test "#broadcast_from broadcasts message on topic, skipping publisher" do
+  test "#broadcast_from and #broadcast_from! broadcasts message, skipping publisher" do
     socket = new_socket |> Socket.put_topic("top:subtop")
     PubSub.subscribe(:my_app_pub, socket.pid, "top:subtop")
 
     assert Channel.broadcast_from(:my_app_pub, socket, "event", %{payload: "hello"})
     refute Enum.any?(Process.info(self)[:messages], &match?(%Message{}, &1))
+
+    assert Channel.broadcast_from!(:my_app_pub, socket, "event", %{payload: "hello"})
+    refute Enum.any?(Process.info(self)[:messages], &match?(%Message{}, &1))
   end
 
-  test "#broadcast_from raises friendly error when message arg isn't a Map" do
+  test "#broadcast_from and #broadcast_from! raises error when msg isn't a Map" do
     socket = Socket.put_topic(new_socket, "top:subtop")
     message = "Message argument must be a map"
     assert_raise RuntimeError, message, fn ->
       Channel.broadcast_from(:my_app_pub, socket, "event", bar: "foo", foo: "bar")
     end
+    assert_raise RuntimeError, message, fn ->
+      Channel.broadcast_from!(:my_app_pub, socket, "event", bar: "foo", foo: "bar")
+    end
   end
 
-  test "#broadcast_from/4 raises friendly error when message arg isn't a Map" do
+  test "#broadcast_from/4 and broadcast_from!/4 raises error when msg isn't a Map" do
     message = "Message argument must be a map"
     assert_raise RuntimeError, message, fn ->
       Channel.broadcast_from(:my_app_pub, self, "topic:subtopic", "event", bar: "foo")
     end
+    assert_raise RuntimeError, message, fn ->
+      Channel.broadcast_from!(:my_app_pub, self, "topic:subtopic", "event", bar: "foo")
+    end
   end
 
   test "#reply sends response to socket" do
diff --git a/test/phoenix/integration/channel_test.exs b/test/phoenix/integration/channel_test.exs
index 428cf85a93..02a9758bc4 100644
--- a/test/phoenix/integration/channel_test.exs
+++ b/test/phoenix/integration/channel_test.exs
@@ -36,7 +36,7 @@ defmodule Phoenix.Integration.ChannelTest do
     end
 
     def handle_in("new:msg", message, socket) do
-      broadcast socket, "new:msg", message
+      broadcast! socket, "new:msg", message
     end
   end
 
@@ -149,8 +149,8 @@ defmodule Phoenix.Integration.ChannelTest do
     assert resp.status == 204
 
     # messages are buffered between polls
-    Phoenix.Channel.broadcast :my_app_pub, "rooms:lobby", "user:entered", %{name: "José"}
-    Phoenix.Channel.broadcast :my_app_pub, "rooms:lobby", "user:entered", %{name: "Sonny"}
+    Phoenix.Channel.broadcast! :my_app_pub, "rooms:lobby", "user:entered", %{name: "José"}
+    Phoenix.Channel.broadcast! :my_app_pub, "rooms:lobby", "user:entered", %{name: "Sonny"}
     {resp, cookie} = poll(:get, "/ws/poll", cookie)
     assert resp.status == 200
     assert Enum.count(resp.body) == 2
@@ -190,7 +190,7 @@ defmodule Phoenix.Integration.ChannelTest do
                                                          "event" => "join",
                                                          "payload" => %{}}
       assert resp.status == 200
-      Phoenix.Channel.broadcast :my_app_pub, "rooms:lobby", "new:msg", %{body: "Hello lobby"}
+      Phoenix.Channel.broadcast! :my_app_pub, "rooms:lobby", "new:msg", %{body: "Hello lobby"}
       # poll
       {resp, cookie} = poll(:get, "/ws/poll", cookie)
       assert resp.status == 200
diff --git a/test/phoenix/pubsub/pubsub_test.exs b/test/phoenix/pubsub/pubsub_test.exs
index bc62f2c81c..2d4db28289 100644
--- a/test/phoenix/pubsub/pubsub_test.exs
+++ b/test/phoenix/pubsub/pubsub_test.exs
@@ -12,6 +12,11 @@ defmodule Phoenix.PubSub.PubSubTest do
     spawn fn -> :timer.sleep(:infinity) end
   end
 
+  defmodule FailedBroadcaster do
+    def broadcast(_server, _topic, _msg), do: {:error, :boom}
+    def broadcast_from(_server, _from_pid, _topic, _msg), do: {:error, :boom}
+  end
+
   for {adapter, name} <- @adapters do
     @adapter adapter
     @server name
@@ -63,25 +68,42 @@ defmodule Phoenix.PubSub.PubSubTest do
       assert Process.alive?(non_linked_pid2)
     end
 
-    test "#{inspect @adapter} #broadcast publishes message to each subscriber" do
+    test "#{inspect @adapter} broadcast/3 and broadcast!/3 publishes message to each subscriber" do
       PubSub.subscribe(@server, self, "topic9")
       assert PubSub.subscribers(@server, "topic9") |> Enum.to_list == [self]
-      PubSub.broadcast(@server, "topic9", :ping)
+      :ok = PubSub.broadcast(@server, "topic9", :ping)
+      assert_receive :ping
+      :ok = PubSub.broadcast!(@server, "topic9", :ping)
       assert_receive :ping
     end
 
-    test "#{inspect @adapter} #broadcast does not publish message to other topic subscribers" do
+    test "#{inspect @adapter} broadcast!/3 and broadcast_from!/4 raise if broadcast fails" do
+      PubSub.subscribe(@server, self, "topic9")
+      assert PubSub.subscribers(@server, "topic9") |> Enum.to_list == [self]
+      assert_raise PubSub.BroadcastError, fn ->
+        PubSub.broadcast!(@server, "topic9", :ping, FailedBroadcaster)
+      end
+      assert_raise PubSub.BroadcastError, fn ->
+        PubSub.broadcast_from!(@server, self, "topic9", :ping, FailedBroadcaster)
+      end
+      refute_receive :ping
+    end
+
+    test "#{inspect @adapter} broadcast/3 does not publish message to other topic subscribers" do
       pids = Enum.map 0..10, fn _ -> spawn_pid end
       pids |> Enum.each(&PubSub.subscribe(@server, &1, "topic10"))
-      PubSub.broadcast(@server, "topic10", :ping)
+      :ok = PubSub.broadcast(@server, "topic10", :ping)
       refute_receive :ping
       pids |> Enum.each(&Process.exit &1, :kill)
     end
 
-    test "#{inspect @adapter} #broadcast_from does not publish to broadcaster pid when provided" do
+    test "#{inspect @adapter} broadcast_from/4 and broadcast_from!/4 skips sender" do
       PubSub.subscribe(@server, self, "topic11")
       PubSub.broadcast_from(@server, self, "topic11", :ping)
       refute_receive :ping
+
+      PubSub.broadcast_from!(@server, self, "topic11", :ping)
+      refute_receive :ping
     end
 
     test "#{inspect @adapter} processes automatically removed from topic when killed" do