diff --git a/app/assets/javascripts/discourse/controllers/preferences/interface.js.es6 b/app/assets/javascripts/discourse/controllers/preferences/interface.js.es6
index 97cab16b0db..c9b8d796e71 100644
--- a/app/assets/javascripts/discourse/controllers/preferences/interface.js.es6
+++ b/app/assets/javascripts/discourse/controllers/preferences/interface.js.es6
@@ -20,6 +20,8 @@ const USER_HOMES = {
   5: "top"
 };
 
+const TEXT_SIZES = ["normal", "larger", "largest"];
+
 export default Ember.Controller.extend(PreferencesTabController, {
   @computed("makeThemeDefault")
   saveAttrNames(makeDefault) {
@@ -32,7 +34,8 @@ export default Ember.Controller.extend(PreferencesTabController, {
       "automatically_unpin_topics",
       "allow_private_messages",
       "homepage_id",
-      "hide_profile_and_presence"
+      "hide_profile_and_presence",
+      "text_size"
     ];
 
     if (makeDefault) {
@@ -55,6 +58,13 @@ export default Ember.Controller.extend(PreferencesTabController, {
     return currentThemeId();
   },
 
+  @computed
+  textSizes() {
+    return TEXT_SIZES.map(value => {
+      return { name: I18n.t(`user.text_size.${value}`), value };
+    });
+  },
+
   userSelectableThemes: function() {
     return listThemes(this.site);
   }.property(),
@@ -114,6 +124,22 @@ export default Ember.Controller.extend(PreferencesTabController, {
           this.homeChanged();
         })
         .catch(popupAjaxError);
+    },
+
+    selectTextSize(newSize) {
+      const classList = document.documentElement.classList;
+
+      TEXT_SIZES.forEach(name => {
+        const className = `text-size-${name}`;
+        if (newSize === name) {
+          classList.add(className);
+        } else {
+          classList.remove(className);
+        }
+      });
+
+      // Force refresh when leaving this screen
+      Discourse.set("assetVersion", "forceRefresh");
     }
   }
 });
diff --git a/app/assets/javascripts/discourse/models/user.js.es6 b/app/assets/javascripts/discourse/models/user.js.es6
index 9b7d28e1ac4..70b6dbc7acd 100644
--- a/app/assets/javascripts/discourse/models/user.js.es6
+++ b/app/assets/javascripts/discourse/models/user.js.es6
@@ -285,7 +285,8 @@ const User = RestModel.extend({
       "theme_ids",
       "allow_private_messages",
       "homepage_id",
-      "hide_profile_and_presence"
+      "hide_profile_and_presence",
+      "text_size"
     ];
 
     if (fields) {
diff --git a/app/assets/javascripts/discourse/templates/preferences/interface.hbs b/app/assets/javascripts/discourse/templates/preferences/interface.hbs
index da84c8c605a..1be49ff9b54 100644
--- a/app/assets/javascripts/discourse/templates/preferences/interface.hbs
+++ b/app/assets/javascripts/discourse/templates/preferences/interface.hbs
@@ -10,6 +10,13 @@
 </div>
 {{/if}}
 
+<div class="control-group text-size">
+  <label class="control-label">{{i18n 'user.text_size.title'}}</label>
+  <div class="controls">
+    {{combo-box valueAttribute="value" content=textSizes value=model.user_option.text_size onSelect=(action "selectTextSize")}}
+  </div>
+</div>
+
 {{#if siteSettings.allow_user_locale}}
   <div class="control-group pref-locale">
     <label class="control-label">{{i18n 'user.locale.title'}}</label>
diff --git a/app/assets/stylesheets/common/foundation/base.scss b/app/assets/stylesheets/common/foundation/base.scss
index 03fa374c22e..adf847650bc 100644
--- a/app/assets/stylesheets/common/foundation/base.scss
+++ b/app/assets/stylesheets/common/foundation/base.scss
@@ -13,6 +13,14 @@ html {
   background-color: $secondary;
   overflow-y: scroll;
   direction: ltr;
+
+  &.text-size-larger {
+    font-size: $base-font-size-larger;
+  }
+
+  &.text-size-largest {
+    font-size: $base-font-size-largest;
+  }
 }
 
 // Links
diff --git a/app/assets/stylesheets/common/foundation/variables.scss b/app/assets/stylesheets/common/foundation/variables.scss
index e0da4fcdaf3..b2090ddd3f8 100644
--- a/app/assets/stylesheets/common/foundation/variables.scss
+++ b/app/assets/stylesheets/common/foundation/variables.scss
@@ -33,6 +33,8 @@ $bronze: #cd7f32 !default;
 // --------------------------------------------------
 
 $base-font-size: 14px !default;
+$base-font-size-larger: 16px !default;
+$base-font-size-largest: 18px !default;
 $base-font-family: Helvetica, Arial, sans-serif !default;
 
 // Font-size defintions, multiplier ^ (step / interval)
diff --git a/app/helpers/application_helper.rb b/app/helpers/application_helper.rb
index 82a5d5fbae6..d4a60fe613e 100644
--- a/app/helpers/application_helper.rb
+++ b/app/helpers/application_helper.rb
@@ -109,7 +109,12 @@ module ApplicationHelper
   end
 
   def html_classes
-    "#{mobile_view? ? 'mobile-view' : 'desktop-view'} #{mobile_device? ? 'mobile-device' : 'not-mobile-device'} #{rtl_class} #{current_user ? '' : 'anon'}"
+    list = []
+    list << (mobile_view? ? 'mobile-view' : 'desktop-view')
+    list << (mobile_device? ? 'mobile-device' : 'not-mobile-device')
+    list << 'rtl' if rtl?
+    list << text_size_class
+    list.join(' ')
   end
 
   def body_classes
@@ -126,8 +131,9 @@ module ApplicationHelper
     result.join(' ')
   end
 
-  def rtl_class
-    rtl? ? 'rtl' : ''
+  def text_size_class
+    size = current_user&.user_option&.text_size || SiteSetting.default_text_size
+    "text-size-#{size}"
   end
 
   def escape_unicode(javascript)
diff --git a/app/models/user_option.rb b/app/models/user_option.rb
index 4f2ba155c89..95b0d75795e 100644
--- a/app/models/user_option.rb
+++ b/app/models/user_option.rb
@@ -28,6 +28,12 @@ class UserOption < ActiveRecord::Base
     @like_notification_frequency_type ||= Enum.new(always: 0, first_time_and_daily: 1, first_time: 2, never: 3)
   end
 
+  def self.text_sizes
+    @text_sizes ||= Enum.new(normal: 0, larger: 1, largest: 2)
+  end
+
+  validates :text_size_key, inclusion: { in: UserOption.text_sizes.values }
+
   def set_defaults
     self.email_always = SiteSetting.default_email_always
     self.mailing_list_mode = SiteSetting.default_email_mailing_list_mode
@@ -58,6 +64,8 @@ class UserOption < ActiveRecord::Base
 
     self.include_tl0_in_digests = SiteSetting.default_include_tl0_in_digests
 
+    self.text_size = SiteSetting.default_text_size
+
     true
   end
 
@@ -146,6 +154,14 @@ class UserOption < ActiveRecord::Base
     end
   end
 
+  def text_size
+    UserOption.text_sizes[text_size_key]
+  end
+
+  def text_size=(value)
+    self.text_size_key = UserOption.text_sizes[value.to_sym]
+  end
+
   private
 
   def update_tracked_topics
@@ -185,6 +201,7 @@ end
 #  homepage_id                      :integer
 #  theme_ids                        :integer          default([]), not null, is an Array
 #  hide_profile_and_presence        :boolean          default(FALSE), not null
+#  text_size_key                    :integer          default(0), not null
 #
 # Indexes
 #
diff --git a/app/serializers/user_option_serializer.rb b/app/serializers/user_option_serializer.rb
index 9df725e84cb..0a0e7048fab 100644
--- a/app/serializers/user_option_serializer.rb
+++ b/app/serializers/user_option_serializer.rb
@@ -23,7 +23,8 @@ class UserOptionSerializer < ApplicationSerializer
              :theme_key_seq,
              :allow_private_messages,
              :homepage_id,
-             :hide_profile_and_presence
+             :hide_profile_and_presence,
+             :text_size
 
   def auto_track_topics_after_msecs
     object.auto_track_topics_after_msecs || SiteSetting.default_other_auto_track_topics_after_msecs
diff --git a/app/services/user_updater.rb b/app/services/user_updater.rb
index 558f08953c4..3828b1da433 100644
--- a/app/services/user_updater.rb
+++ b/app/services/user_updater.rb
@@ -37,7 +37,8 @@ class UserUpdater
     :theme_ids,
     :allow_private_messages,
     :homepage_id,
-    :hide_profile_and_presence
+    :hide_profile_and_presence,
+    :text_size
   ]
 
   def initialize(actor, user)
diff --git a/config/locales/client.en.yml b/config/locales/client.en.yml
index b6d65d54138..a0ab970a488 100644
--- a/config/locales/client.en.yml
+++ b/config/locales/client.en.yml
@@ -909,6 +909,13 @@ en:
       website: "Web Site"
       email_settings: "Email"
       hide_profile_and_presence: "Hide my public profile and presence features"
+
+      text_size:
+        title: "Text Size"
+        normal: "Normal"
+        larger: "Larger"
+        largest: "Largest"
+
       like_notification_frequency:
         title: "Notify when liked"
         always: "Always"
diff --git a/config/locales/server.en.yml b/config/locales/server.en.yml
index 4e3f1224165..8b1742fb678 100644
--- a/config/locales/server.en.yml
+++ b/config/locales/server.en.yml
@@ -1877,6 +1877,8 @@ en:
     default_categories_muted: "List of categories that are muted by default."
     default_categories_watching_first_post: "List of categories in which first post in each new topic will be watched by default."
 
+    default_text_size: "Text size which is selected by default"
+
     retain_web_hook_events_period_days: "Number of days to retain web hook event records."
     retry_web_hook_events: "Automatically retry failed web hook events for 4 times. Time gaps between the retries are 1, 5, 25 and 125 minutes."
 
diff --git a/config/site_settings.yml b/config/site_settings.yml
index 46f838f1cc1..a22ce2a8008 100644
--- a/config/site_settings.yml
+++ b/config/site_settings.yml
@@ -1811,6 +1811,14 @@ user_preferences:
   default_categories_watching_first_post:
     type: category_list
     default: ''
+  
+  default_text_size:
+    type: enum
+    default: normal
+    choices:
+      - normal
+      - larger
+      - largest
 
 api:
   retain_web_hook_events_period_days:
diff --git a/db/migrate/20190108110630_add_text_size_key_to_user_options.rb b/db/migrate/20190108110630_add_text_size_key_to_user_options.rb
new file mode 100644
index 00000000000..61edee561e6
--- /dev/null
+++ b/db/migrate/20190108110630_add_text_size_key_to_user_options.rb
@@ -0,0 +1,5 @@
+class AddTextSizeKeyToUserOptions < ActiveRecord::Migration[5.2]
+  def change
+    add_column :user_options, :text_size_key, :integer, null: false, default: 0
+  end
+end
diff --git a/spec/helpers/application_helper_spec.rb b/spec/helpers/application_helper_spec.rb
index f838326f972..0b1aa0ee6c3 100644
--- a/spec/helpers/application_helper_spec.rb
+++ b/spec/helpers/application_helper_spec.rb
@@ -147,15 +147,29 @@ describe ApplicationHelper do
     end
   end
 
-  describe '#rtl_class' do
-    it "returns 'rtl' when the I18n.locale is rtl" do
+  describe '#html_classes' do
+    it "includes 'rtl' when the I18n.locale is rtl" do
       I18n.stubs(:locale).returns(:he)
-      expect(helper.rtl_class).to eq('rtl')
+      expect(helper.html_classes.split(" ")).to include('rtl')
     end
 
     it 'returns an empty string when the I18n.locale is not rtl' do
       I18n.stubs(:locale).returns(:zh_TW)
-      expect(helper.rtl_class).to eq('')
+      expect(helper.html_classes.split(" ")).not_to include('rtl')
+    end
+
+    it 'includes the user specified text size' do
+      user = Fabricate(:user)
+      user.user_option.text_size = "larger"
+      user.user_option.save!
+      helper.request.env[Auth::DefaultCurrentUserProvider::CURRENT_USER_KEY] = user
+      expect(helper.html_classes.split(" ")).to include('text-size-larger')
+    end
+
+    it 'falls back to the default text size for anon' do
+      expect(helper.html_classes.split(" ")).to include('text-size-normal')
+      SiteSetting.default_text_size = "largest"
+      expect(helper.html_classes.split(" ")).to include('text-size-largest')
     end
   end