diff --git a/_locales/en/messages.json b/_locales/en/messages.json
index 3786e9e47..b4ca335a2 100644
--- a/_locales/en/messages.json
+++ b/_locales/en/messages.json
@@ -324,5 +324,9 @@
     "timestampFormat_M": {
        "description": "Timestamp format string for displaying month and day (but not the year) of a date within the current year, ex: use 'MMM D' for 'Aug 8', or 'D MMM' for '8 Aug'.",
        "message": "MMM D"
+    },
+    "unblockToSend": {
+      "message": "Unblock this contact to send a message.",
+      "description": "Brief message shown when trying to message a blocked number"
     }
 }
diff --git a/background.html b/background.html
index c5d338eef..d90c903b9 100644
--- a/background.html
+++ b/background.html
@@ -479,6 +479,7 @@
   <script type='text/javascript' src='js/libphonenumber-util.js'></script>
   <script type='text/javascript' src='js/models/messages.js'></script>
   <script type='text/javascript' src='js/models/conversations.js'></script>
+  <script type='text/javascript' src='js/models/blockedNumbers.js'></script>
 
   <script type='text/javascript' src='js/chromium.js'></script>
   <script type='text/javascript' src='js/expire.js'></script>
diff --git a/js/libtextsecure.js b/js/libtextsecure.js
index 3e5a033f1..44f1ff3e4 100644
--- a/js/libtextsecure.js
+++ b/js/libtextsecure.js
@@ -38100,7 +38100,10 @@ MessageReceiver.prototype.extend({
             // fault, and we should handle them gracefully and tell the
             // user they received an invalid message
             request.respond(200, 'OK');
-            this.queueEnvelope(envelope);
+
+            if (!this.isBlocked(envelope.source)) {
+                this.queueEnvelope(envelope);
+            }
 
         }.bind(this)).catch(function(e) {
             request.respond(500, 'Bad encrypted websocket message');
@@ -38272,6 +38275,8 @@ MessageReceiver.prototype.extend({
             this.handleContacts(syncMessage.contacts);
         } else if (syncMessage.groups) {
             this.handleGroups(syncMessage.groups);
+        } else if (syncMessage.blocked) {
+            this.handleBlocked(syncMessage.blocked);
         } else if (syncMessage.request) {
             console.log('Got SyncMessage Request');
         } else if (syncMessage.read) {
@@ -38348,6 +38353,12 @@ MessageReceiver.prototype.extend({
             });
         });
     },
+    handleBlocked: function(blocked) {
+        textsecure.storage.put('blocked', blocked.numbers);
+    },
+    isBlocked: function(number) {
+        return textsecure.storage.get('blocked', []).indexOf(number) >= 0;
+    },
     handleAttachment: function(attachment) {
         function decryptAttachment(encrypted) {
             return textsecure.crypto.decryptAttachment(
diff --git a/js/models/blockedNumbers.js b/js/models/blockedNumbers.js
new file mode 100644
index 000000000..76aa6a996
--- /dev/null
+++ b/js/models/blockedNumbers.js
@@ -0,0 +1,10 @@
+/*
+ * vim: ts=4:sw=4:expandtab
+ */
+(function () {
+    'use strict';
+    window.Whisper = window.Whisper || {};
+    storage.isBlocked = function(number) {
+        return storage.get('blocked', []).indexOf(number) >= 0;
+    };
+})();
diff --git a/js/views/conversation_view.js b/js/views/conversation_view.js
index 14d2f4391..13d6e9924 100644
--- a/js/views/conversation_view.js
+++ b/js/views/conversation_view.js
@@ -10,6 +10,11 @@
             return { toastMessage: i18n('expiredWarning') };
         }
     });
+    Whisper.BlockedToast = Whisper.ToastView.extend({
+        render_attributes: function() {
+            return { toastMessage: i18n('unblockToSend') };
+        }
+    });
 
     Whisper.ConversationView = Whisper.View.extend({
         className: function() {
@@ -276,6 +281,12 @@
                 toast.render();
                 return;
             }
+            if (this.model.isPrivate() && storage.isBlocked(this.model.id)) {
+                var toast = new Whisper.BlockedToast();
+                toast.$el.insertAfter(this.$el);
+                toast.render();
+                return;
+            }
             e.preventDefault();
             var input = this.$messageField;
             var message = this.replace_colons(input.val()).trim();
diff --git a/libtextsecure/message_receiver.js b/libtextsecure/message_receiver.js
index 5fed062aa..6e8d98b9b 100644
--- a/libtextsecure/message_receiver.js
+++ b/libtextsecure/message_receiver.js
@@ -70,7 +70,10 @@ MessageReceiver.prototype.extend({
             // fault, and we should handle them gracefully and tell the
             // user they received an invalid message
             request.respond(200, 'OK');
-            this.queueEnvelope(envelope);
+
+            if (!this.isBlocked(envelope.source)) {
+                this.queueEnvelope(envelope);
+            }
 
         }.bind(this)).catch(function(e) {
             request.respond(500, 'Bad encrypted websocket message');
@@ -242,6 +245,8 @@ MessageReceiver.prototype.extend({
             this.handleContacts(syncMessage.contacts);
         } else if (syncMessage.groups) {
             this.handleGroups(syncMessage.groups);
+        } else if (syncMessage.blocked) {
+            this.handleBlocked(syncMessage.blocked);
         } else if (syncMessage.request) {
             console.log('Got SyncMessage Request');
         } else if (syncMessage.read) {
@@ -318,6 +323,12 @@ MessageReceiver.prototype.extend({
             });
         });
     },
+    handleBlocked: function(blocked) {
+        textsecure.storage.put('blocked', blocked.numbers);
+    },
+    isBlocked: function(number) {
+        return textsecure.storage.get('blocked', []).indexOf(number) >= 0;
+    },
     handleAttachment: function(attachment) {
         function decryptAttachment(encrypted) {
             return textsecure.crypto.decryptAttachment(
diff --git a/protos/IncomingPushMessageSignal.proto b/protos/IncomingPushMessageSignal.proto
index 9c780bbca..652a3ebe7 100644
--- a/protos/IncomingPushMessageSignal.proto
+++ b/protos/IncomingPushMessageSignal.proto
@@ -52,11 +52,16 @@ message SyncMessage {
     optional AttachmentPointer blob = 1;
   }
 
+  message Blocked {
+    repeated string numbers = 1;
+  }
+
   message Request {
     enum Type {
       UNKNOWN     = 0;
       CONTACTS    = 1;
       GROUPS      = 2;
+      BLOCKED     = 3;
     }
     optional Type type = 1;
   }
@@ -70,6 +75,7 @@ message SyncMessage {
   optional Groups   groups   = 3;
   optional Request  request  = 4;
   repeated Read     read     = 5;
+  optional Blocked  blocked  = 6;
 }
 
 message AttachmentPointer {