diff --git a/app/assets/javascripts/discourse/components/composer-user-selector.js.es6 b/app/assets/javascripts/discourse/components/composer-user-selector.js.es6
new file mode 100644
index 00000000000..d977d6e3093
--- /dev/null
+++ b/app/assets/javascripts/discourse/components/composer-user-selector.js.es6
@@ -0,0 +1,74 @@
+import { default as computed, observes } from 'ember-addons/ember-computed-decorators';
+
+export default Ember.Component.extend({
+  showSelector: true,
+  shouldHide: false,
+  defaultUsernameCount: 0,
+
+  @observes('usernames')
+  _checkWidth() {
+    let width = 0;
+    const $acWrap = this.$().find('.ac-wrap');
+    const limit = $acWrap.width();
+    this.set('defaultUsernameCount', 0);
+
+    $acWrap.find('.item').toArray().forEach(item => {
+      width += $(item).outerWidth(true);
+      const result = (width < limit);
+
+      if (result) this.incrementProperty('defaultUsernameCount');
+      return result;
+    });
+
+    if (width >= limit) {
+      this.set('shouldHide', true);
+    } else {
+      this.set('shouldHide', false);
+    };
+  },
+
+  @observes('shouldHide')
+  _setFocus() {
+    const selector = '#reply-control #reply-title, #reply-control .d-editor-input';
+
+    if (this.get('shouldHide')) {
+      $(selector).on('focus.composer-user-selector', () => {
+        this.set('showSelector', false);
+        this.appEvents.trigger("composer:resize");
+      });
+    } else {
+      $(selector).off('focus.composer-user-selector');
+    }
+  },
+
+  @computed('usernames')
+  splitUsernames(usernames) {
+    return usernames.split(',');
+  },
+
+  @computed('splitUsernames', 'defaultUsernameCount')
+  limitedUsernames(splitUsernames, count) {
+    return splitUsernames.slice(0, count).join(", ");
+  },
+
+  @computed('splitUsernames', 'defaultUsernameCount')
+  hiddenUsersCount(splitUsernames, count) {
+    return `${splitUsernames.length - count} ${I18n.t('more')}`;
+  },
+
+  actions: {
+    toggleSelector() {
+      this.set("showSelector", true);
+
+      Ember.run.schedule('afterRender', () => {
+        this.$().find('input').focus();
+      });
+    },
+
+    triggerResize() {
+      this.appEvents.trigger("composer:resize");
+      const $this = this.$().find('.ac-wrap');
+      if ($this.height() >= 150) $this.scrollTop($this.height());
+    },
+  }
+});
diff --git a/app/assets/javascripts/discourse/components/user-selector.js.es6 b/app/assets/javascripts/discourse/components/user-selector.js.es6
index ab695e8b2b0..862f0fae491 100644
--- a/app/assets/javascripts/discourse/components/user-selector.js.es6
+++ b/app/assets/javascripts/discourse/components/user-selector.js.es6
@@ -1,9 +1,11 @@
+import { observes } from 'ember-addons/ember-computed-decorators';
 import TextField from 'discourse/components/text-field';
 import userSearch from 'discourse/lib/user-search';
 
 export default TextField.extend({
 
-  _initializeAutocomplete: function() {
+  didInsertElement() {
+    this._super();
     var self = this,
         selected = [],
         groups = [],
@@ -63,6 +65,7 @@ export default TextField.extend({
         self.set('hasGroups', hasGroups);
 
         selected = items;
+        if (self.get('onChangeCallback')) self.sendAction('onChangeCallback');
       },
 
       reverseTransform: function(i) {
@@ -70,19 +73,21 @@ export default TextField.extend({
       }
 
     });
-  }.on('didInsertElement'),
+  },
 
-  _removeAutocomplete: function() {
+  willDestroyElement() {
+    this._super();
     this.$().autocomplete('destroy');
-  }.on('willDestroyElement'),
+  },
 
   // THIS IS A HUGE HACK TO SUPPORT CLEARING THE INPUT
+  @observes('usernames')
   _clearInput: function() {
     if (arguments.length > 1) {
       if (Em.isEmpty(this.get("usernames"))) {
         this.$().parent().find("a").click();
       }
     }
-  }.observes("usernames")
+  }
 
 });
diff --git a/app/assets/javascripts/discourse/lib/autocomplete.js.es6 b/app/assets/javascripts/discourse/lib/autocomplete.js.es6
index a142947da65..a2edb6b886b 100644
--- a/app/assets/javascripts/discourse/lib/autocomplete.js.es6
+++ b/app/assets/javascripts/discourse/lib/autocomplete.js.es6
@@ -101,13 +101,16 @@ export default function(options) {
     transformed = _.isArray(transformedItem) ? transformedItem : [transformedItem || item];
 
     var divs = transformed.map(function(itm) {
-      var d = $("<div class='item'><span>" + itm + "<a class='remove' href><i class='fa fa-times'></i></a></span></div>");
-      var prev = me.parent().find('.item:last');
+      let d = $(`<div class='item'><span>${itm}<a class='remove' href><i class='fa fa-times'></i></a></span></div>`);
+      const $parent = me.parent();
+      const prev = $parent.find('.item:last');
+
       if (prev.length === 0) {
         me.parent().prepend(d);
       } else {
         prev.after(d);
       }
+
       inputSelectedItems.push(itm);
       return d[0];
     });
diff --git a/app/assets/javascripts/discourse/templates/components/composer-user-selector.hbs b/app/assets/javascripts/discourse/templates/components/composer-user-selector.hbs
new file mode 100644
index 00000000000..71b5e8176d2
--- /dev/null
+++ b/app/assets/javascripts/discourse/templates/components/composer-user-selector.hbs
@@ -0,0 +1,17 @@
+{{#if showSelector}}
+  {{user-selector topicId=topicId
+                  excludeCurrentUser='true'
+                  onChangeCallback='triggerResize'
+                  id="private-message-users"
+                  includeMentionableGroups='true'
+                  class="span8"
+                  placeholderKey="composer.users_placeholder"
+                  tabindex="1"
+                  usernames=usernames
+                  hasGroups=hasGroups}}
+{{else}}
+  <div class='ac-wrap composer-user-selector-limited' {{action "toggleSelector"}}>
+    <span>{{limitedUsernames}}</span>
+    <span class='btn-small btn-primary'>{{hiddenUsersCount}}</span>
+  </div>
+{{/if}}
diff --git a/app/assets/javascripts/discourse/templates/composer.hbs b/app/assets/javascripts/discourse/templates/composer.hbs
index 290a0815bdc..4471943e168 100644
--- a/app/assets/javascripts/discourse/templates/composer.hbs
+++ b/app/assets/javascripts/discourse/templates/composer.hbs
@@ -48,13 +48,7 @@
           {{#if model.canEditTitle}}
             <div class='form-element clearfix'>
               {{#if model.creatingPrivateMessage}}
-                {{user-selector topicId=topicModel.id
-                                excludeCurrentUser="true"
-                                id="private-message-users"
-                                includeMentionableGroups="true"
-                                class="span8"
-                                placeholderKey="composer.users_placeholder"
-                                tabindex="1"
+                {{composer-user-selector topicId=topicModel.id
                                 usernames=model.targetUsernames
                                 hasGroups=model.hasTargetGroups
                                 }}
diff --git a/app/assets/javascripts/discourse/views/composer.js.es6 b/app/assets/javascripts/discourse/views/composer.js.es6
index 5d6924718b1..0542b6d8da7 100644
--- a/app/assets/javascripts/discourse/views/composer.js.es6
+++ b/app/assets/javascripts/discourse/views/composer.js.es6
@@ -103,6 +103,13 @@ const ComposerView = Ember.View.extend({
       triggerOpen();
     });
     positioningWorkaround(this.$());
+
+    this.appEvents.on('composer:resize', this, this.resize);
+  },
+
+  willDestroyElement() {
+    this._super();
+    this.appEvents.off('composer:resize', this, this.resize);
   },
 
   click() {
diff --git a/app/assets/stylesheets/common/base/compose.scss b/app/assets/stylesheets/common/base/compose.scss
index 4bb02e82ddd..dfadbd6fb80 100644
--- a/app/assets/stylesheets/common/base/compose.scss
+++ b/app/assets/stylesheets/common/base/compose.scss
@@ -97,6 +97,8 @@ div.ac-wrap div.item a.remove, .remove-link {
 }
 
 div.ac-wrap {
+  overflow: auto;
+  max-height: 150px;
   background-color: $secondary;
   border: 1px solid dark-light-diff($primary, $secondary, 90%, -60%);
   padding: 5px 4px 1px 4px;
@@ -110,6 +112,15 @@ div.ac-wrap {
       line-height: 20px;
     }
   }
+
+  .ac-collapsed-button {
+    float: left;
+    border-radius: 20px;
+    position: relative;
+    top: -2px;
+    margin-right: 10px;
+  }
+
   input[type="text"] {
     float: left;
     margin-bottom: 4px;
diff --git a/app/assets/stylesheets/common/base/composer-user-selector.scss b/app/assets/stylesheets/common/base/composer-user-selector.scss
new file mode 100644
index 00000000000..f3ea48c8abf
--- /dev/null
+++ b/app/assets/stylesheets/common/base/composer-user-selector.scss
@@ -0,0 +1,10 @@
+div.ac-wrap.composer-user-selector-limited {
+  width: 400px;
+
+  .btn-small {
+    border-radius: 10px;
+    position: relative;
+    top: -2px;
+    float: none;
+  }
+}