diff --git a/app/helpers/application_helper.rb b/app/helpers/application_helper.rb
index 9fb6a56c2..bff3cd2a0 100644
--- a/app/helpers/application_helper.rb
+++ b/app/helpers/application_helper.rb
@@ -53,7 +53,8 @@ module ApplicationHelper
       name = h(user.name(options[:format]))
       if user.active? || (User.current.admin? && user.logged?)
         only_path = options[:only_path].nil? ? true : options[:only_path]
-        link_to name, user_url(user, :only_path => only_path), :class => user.css_classes
+        css_classes = options[:class] ? "#{user.css_classes} #{options[:class]}" : user.css_classes
+        link_to name, user_url(user, :only_path => only_path), :class => css_classes
       else
         name
       end
@@ -1080,9 +1081,6 @@ module ApplicationHelper
               if p = Project.visible.find_by_id(oid)
                 link = link_to_project(p, {:only_path => only_path}, :class => 'project')
               end
-            when 'user'
-              u = User.visible.find_by(:id => oid, :type => 'User')
-              link = link_to_user(u, :only_path => only_path) if u
             end
           elsif sep == ':'
             name = remove_double_quotes(identifier)
@@ -1157,14 +1155,14 @@ module ApplicationHelper
               if p = Project.visible.where("identifier = :s OR LOWER(name) = :s", :s => name.downcase).first
                 link = link_to_project(p, {:only_path => only_path}, :class => 'project')
               end
-            when 'user'
-              u = User.visible.find_by("LOWER(login) = :s AND type = 'User'", :s => name.downcase)
-              link = link_to_user(u, :only_path => only_path) if u
             end
-          elsif sep == "@"
-            name = remove_double_quotes(identifier)
-            u = User.visible.find_by("LOWER(login) = :s AND type = 'User'", :s => name.downcase)
-            link = link_to_user(u, :only_path => only_path) if u
+          end
+          if link.nil? && $~
+            user = User.mentioned_user($~.named_captures.symbolize_keys)
+            if user
+              css_classes = (user.notify_mentioned_user?(obj) ? 'notified' : nil)
+              link = link_to_user(user, :only_path => only_path, :class => css_classes)
+            end
           end
         end
         (leading + (link || "#{project_prefix}#{prefix}#{repo_prefix}#{sep}#{identifier}#{comment_suffix}"))
diff --git a/app/models/comment.rb b/app/models/comment.rb
index 3e7005280..f6b485958 100644
--- a/app/models/comment.rb
+++ b/app/models/comment.rb
@@ -24,6 +24,8 @@ class Comment < ActiveRecord::Base
 
   validates_presence_of :commented, :author, :content
 
+  acts_as_mentionable :attributes => ['content']
+
   after_create_commit :send_notification
 
   safe_attributes 'comments'
diff --git a/app/models/document.rb b/app/models/document.rb
index 4f562fc70..5cc89de4d 100644
--- a/app/models/document.rb
+++ b/app/models/document.rb
@@ -63,7 +63,7 @@ class Document < ActiveRecord::Base
   end
 
   def notified_users
-    project.notified_users.reject {|user| !visible?(user)}
+    project.notified_users.select {|user| user.allowed_to_view_notify_target?(self) }
   end
 
   private
diff --git a/app/models/issue.rb b/app/models/issue.rb
index 63bc8cabe..053179d2c 100644
--- a/app/models/issue.rb
+++ b/app/models/issue.rb
@@ -43,6 +43,7 @@ class Issue < ActiveRecord::Base
   acts_as_attachable :after_add => :attachment_added, :after_remove => :attachment_removed
   acts_as_customizable
   acts_as_watchable
+  acts_as_mentionable :attributes => ['description']
   acts_as_searchable :columns => ['subject', "#{table_name}.description"],
                      :preload => [:project, :status, :tracker],
                      :scope => lambda {|options| options[:open_issues] ? self.open : self.all}
@@ -1045,8 +1046,7 @@ class Issue < ActiveRecord::Base
     notified += project.users.preload(:preference).select(&:notify_about_high_priority_issues?) if priority.high?
     notified.uniq!
     # Remove users that can not view the issue
-    notified.reject! {|user| !visible?(user)}
-    notified
+    notified.select {|user| user.allowed_to_view_notify_target?(self)}
   end
 
   # Returns the email addresses that should be notified
diff --git a/app/models/journal.rb b/app/models/journal.rb
index 191fac972..cca190cec 100644
--- a/app/models/journal.rb
+++ b/app/models/journal.rb
@@ -29,13 +29,13 @@ class Journal < ActiveRecord::Base
   has_many :details, :class_name => "JournalDetail", :dependent => :delete_all, :inverse_of => :journal
   attr_accessor :indice
 
+  acts_as_mentionable :attributes => ['notes']
   acts_as_event :title => Proc.new {|o| status = ((s = o.new_status) ? " (#{s})" : nil); "#{o.issue.tracker} ##{o.issue.id}#{status}: #{o.issue.subject}" },
                 :description => :notes,
                 :author => :user,
                 :group => :issue,
                 :type => Proc.new {|o| (s = o.new_status) ? (s.is_closed? ? 'issue-closed' : 'issue-edit') : 'issue-note' },
                 :url => Proc.new {|o| {:controller => 'issues', :action => 'show', :id => o.issue.id, :anchor => "change-#{o.id}"}}
-
   acts_as_activity_provider :type => 'issues',
                             :author_key => :user_id,
                             :scope => preload({:issue => :project}, :user).
@@ -145,10 +145,7 @@ class Journal < ActiveRecord::Base
 
   def notified_users
     notified = journalized.notified_users
-    if private_notes?
-      notified = notified.select {|user| user.allowed_to?(:view_private_notes, journalized.project)}
-    end
-    notified
+    notified.select{ |u| u.allowed_to_view_notify_target?(self) }
   end
 
   def recipients
diff --git a/app/models/mailer.rb b/app/models/mailer.rb
index 550c149cb..065c42f60 100644
--- a/app/models/mailer.rb
+++ b/app/models/mailer.rb
@@ -93,6 +93,7 @@ class Mailer < ActionMailer::Base
   #   Mailer.deliver_issue_add(issue)
   def self.deliver_issue_add(issue)
     users = issue.notified_users | issue.notified_watchers
+    users -= issue.mentioned_users_with_latest_changes
     users.each do |user|
       issue_add(user, issue).deliver_later
     end
@@ -131,6 +132,9 @@ class Mailer < ActionMailer::Base
     users.select! do |user|
       journal.notes? || journal.visible_details(user).any?
     end
+    users -= journal.mentioned_users_with_latest_changes
+    users -= journal.issue.mentioned_users_with_latest_changes
+
     users.each do |user|
       issue_edit(user, journal).deliver_later
     end
@@ -221,6 +225,7 @@ class Mailer < ActionMailer::Base
   #   Mailer.deliver_news_added(news)
   def self.deliver_news_added(news)
     users = news.notified_users | news.notified_watchers_for_added_news
+    users -= news.mentioned_users_with_latest_changes
     users.each do |user|
       news_added(user, news).deliver_later
     end
@@ -248,6 +253,7 @@ class Mailer < ActionMailer::Base
   def self.deliver_news_comment_added(comment)
     news = comment.commented
     users = news.notified_users | news.notified_watchers
+    users -= comment.mentioned_users_with_latest_changes
     users.each do |user|
       news_comment_added(user, comment).deliver_later
     end
@@ -275,6 +281,7 @@ class Mailer < ActionMailer::Base
     users  = message.notified_users
     users |= message.root.notified_watchers
     users |= message.board.notified_watchers
+    users -= message.mentioned_users_with_latest_changes
 
     users.each do |user|
       message_posted(user, message).deliver_later
@@ -529,6 +536,22 @@ class Mailer < ActionMailer::Base
     end
   end
 
+  def mail_to_mentioned_users(user, obj, contents)
+    @contents = contents
+    mail :to => user,
+         :subject => "You are mentioned by #{obj.try(:author) || obj.user} in #{obj.class}##{obj.id}"
+  end
+
+  # Notifies mentioned users.
+  #
+  # Example:
+  #   Mailer.deliver_mail_to_mentioned_users(users, obj, content)
+  def self.deliver_mail_to_mentioned_users(users, obj, content)
+    users.each do |user|
+      mail_to_mentioned_users(user, obj, content).deliver_later
+    end
+  end
+
   # Build a test email to user.
   def test_email(user)
     @url = url_for(:controller => 'welcome')
diff --git a/app/models/message.rb b/app/models/message.rb
index f48785447..a1e1221c3 100644
--- a/app/models/message.rb
+++ b/app/models/message.rb
@@ -114,7 +114,7 @@ class Message < ActiveRecord::Base
   end
 
   def notified_users
-    project.notified_users.reject {|user| !visible?(user)}
+    project.notified_users.select {|user| user.allowed_to_view_notify_target?(self) }
   end
 
   private
diff --git a/app/models/news.rb b/app/models/news.rb
index 3ad43bff7..3069d202c 100644
--- a/app/models/news.rb
+++ b/app/models/news.rb
@@ -31,6 +31,7 @@ class News < ActiveRecord::Base
                      :delete_permission => :manage_news
   acts_as_searchable :columns => ['title', 'summary', "#{table_name}.description"],
                      :preload => :project
+  acts_as_mentionable :attributes => ['description']
   acts_as_event :url => Proc.new {|o| {:controller => 'news', :action => 'show', :id => o.id}}
   acts_as_activity_provider :scope => preload(:project, :author),
                             :author_key => :author_id
@@ -56,7 +57,7 @@ class News < ActiveRecord::Base
   end
 
   def notified_users
-    project.users.select {|user| user.notify_about?(self) && user.allowed_to?(:view_news, project)}
+    project.users.select {|user| user.notify_about?(self) && user.allowed_to_view_notify_target?(self)}
   end
 
   def recipients
diff --git a/app/models/user.rb b/app/models/user.rb
index 76f479bcd..09839d221 100644
--- a/app/models/user.rb
+++ b/app/models/user.rb
@@ -823,6 +823,47 @@ class User < Principal
     RequestStore.store[:current_user] ||= User.anonymous
   end
 
+  # Return the mentioned user to based on the match data
+  #  of ApplicationHelper::LINKS_RE.
+  #     user:jsmith -> Link to user with login jsmith
+  #     @jsmith -> Link to user with login jsmith
+  #     user#2 -> Link to user with id 2
+  def self.mentioned_user(match_data)
+    return nil if match_data[:esc]
+    sep = match_data[:sep1] || match_data[:sep2] || match_data[:sep3] || match_data[:sep4]
+    identifier = match_data[:identifier1] || match_data[:identifier2] || match_data[:identifier3]
+    prefix = match_data[:prefix]
+    if ['#', '##'].include?(sep) && prefix == 'user'
+      User.visible.find_by(:id => identifier.to_i, :type => 'User')
+    elsif sep == '@' || (sep == ':' && prefix == 'user')
+      name = identifier.gsub(%r{^"(.*)"$}, "\\1")
+      User.find_by_login(CGI.unescapeHTML(name).downcase)
+    end
+  end
+
+  # Return true if notify the mentioned user.
+  def notify_mentioned_user?(object)
+    self.active? &&
+      self.mail.present? &&
+      self.mail_notification.present? && self.mail_notification != 'none' &&
+      self.allowed_to_view_notify_target?(object)
+  end
+
+  # Return true if the user is allowed to view the notify target.
+  def allowed_to_view_notify_target?(object)
+    case object
+    when Journal
+      self.allowed_to_view_notify_target?(object.journalized) &&
+        (!object.private_notes? || self.allowed_to?(:view_private_notes, object.journalized.project))
+    when Comment
+      self.allowed_to_view_notify_target?(object.commented)
+    when nil
+      false
+    else
+      object.visible?(self)
+    end
+  end
+
   # Returns the anonymous user.  If the anonymous user does not exist, it is created.  There can be only
   # one anonymous user per database.
   def self.anonymous
diff --git a/app/models/wiki_content.rb b/app/models/wiki_content.rb
index d38c5ca7d..ef2c28c5a 100644
--- a/app/models/wiki_content.rb
+++ b/app/models/wiki_content.rb
@@ -53,7 +53,7 @@ class WikiContent < ActiveRecord::Base
   end
 
   def notified_users
-    project.notified_users.reject {|user| !visible?(user)}
+    project.notified_users.select {|user| user.allowed_to_view_notify_target?(self) }
   end
 
   # Returns the mail addresses of users that should be notified
diff --git a/app/views/mailer/mail_to_mentioned_users.html.erb b/app/views/mailer/mail_to_mentioned_users.html.erb
new file mode 100644
index 000000000..ec63cf874
--- /dev/null
+++ b/app/views/mailer/mail_to_mentioned_users.html.erb
@@ -0,0 +1,3 @@
+<% @contents.each do |key, content| %>
+<p><%= textilizable content %></p>
+<% end %>
\ No newline at end of file
diff --git a/app/views/mailer/mail_to_mentioned_users.text.erb b/app/views/mailer/mail_to_mentioned_users.text.erb
new file mode 100644
index 000000000..53a7c2eb3
--- /dev/null
+++ b/app/views/mailer/mail_to_mentioned_users.text.erb
@@ -0,0 +1,3 @@
+<% @contents.each do |key, content| %>
+<%= textilizable content %>
+<% end %>
\ No newline at end of file
diff --git a/lib/plugins/acts_as_mentionable/init.rb b/lib/plugins/acts_as_mentionable/init.rb
new file mode 100644
index 000000000..248383f3c
--- /dev/null
+++ b/lib/plugins/acts_as_mentionable/init.rb
@@ -0,0 +1,5 @@
+# frozen_string_literal: true
+
+# Include hook code here
+require File.dirname(__FILE__) + '/lib/acts_as_mentionable'
+ActiveRecord::Base.send(:include, Redmine::Acts::Mentionable)
diff --git a/lib/plugins/acts_as_mentionable/lib/acts_as_mentionable.rb b/lib/plugins/acts_as_mentionable/lib/acts_as_mentionable.rb
new file mode 100644
index 000000000..f4f884a98
--- /dev/null
+++ b/lib/plugins/acts_as_mentionable/lib/acts_as_mentionable.rb
@@ -0,0 +1,86 @@
+# frozen_string_literal: true
+
+# Redmine - project management software
+# Copyright (C) 2006-2019  Jean-Philippe Lang
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License
+# as published by the Free Software Foundation; either version 2
+# of the License, or (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+
+module Redmine
+  module Acts
+    module Mentionable
+      def self.included(base)
+        base.extend ClassMethods
+      end
+
+      module ClassMethods
+        def acts_as_mentionable(options = {})
+          return if self.included_modules.include?(Redmine::Acts::Mentionable::InstanceMethods)
+
+          cattr_accessor :mentionable_attributes
+          self.mentionable_attributes = options[:attributes]
+
+          send :include, Redmine::Acts::Mentionable::InstanceMethods
+
+          before_save :was_new_record?
+          after_save :notify_mentioned_users
+        end
+      end
+
+      module InstanceMethods
+        def self.included(base)
+          base.extend ClassMethods
+        end
+
+        def was_new_record?
+          @was_new_record = self.new_record?
+        end
+
+        def notify_mentioned_users
+          attribute_values = mentionable_attributes.map{|attr| [attr, self.saved_changes[attr][1]] if self.saved_changes[attr] }.compact.to_h
+          users = mentioned_users_with_latest_changes
+          Mailer.deliver_mail_to_mentioned_users(users, self, attribute_values) if users.present?
+        end
+
+        def mentioned_users_with_latest_changes
+          changes = self.saved_changes
+          if @was_new_record
+            values = mentionable_attributes.map{|attr| changes[attr] && changes[attr][1] }.compact
+            users = mentioned_users(values)
+          else
+            new_values = mentionable_attributes.map{|attr| changes[attr] && changes[attr][1] }.compact
+            old_values = mentionable_attributes.map{|attr| changes[attr] && changes[attr][0] }.compact
+            users = mentioned_users(new_values) - mentioned_users(old_values)
+          end
+          users
+        end
+
+        def mentioned_users(values)
+          users = []
+          values.each do |value|
+            value.scan(ApplicationHelper::LINKS_RE) do |_|
+              target = User.mentioned_user($~.named_captures.symbolize_keys)
+              next if target.blank? || users.include?(target)
+              users << target if target.notify_mentioned_user?(self)
+            end
+          end
+          users.uniq
+        end
+
+        module ClassMethods
+        end
+      end
+    end
+  end
+end
diff --git a/public/stylesheets/application.css b/public/stylesheets/application.css
index 346705efe..f4a578eb9 100644
--- a/public/stylesheets/application.css
+++ b/public/stylesheets/application.css
@@ -137,6 +137,7 @@ div.modal .box p {margin: 0.3em 0;}
 a, a:link, a:visited{ color: #169; text-decoration: none; }
 a:hover, a:active{ color: #c61a1a; text-decoration: underline;}
 a img{ border: 0; }
+a.user.notified, a.user.notified:link, a.user.notified:visited {padding: 2px; border-radius: 3px; background-color: #bae9f5}
 
 a.issue.closed, a.issue.closed:link, a.issue.closed:visited { color: #999; text-decoration: line-through; }
 a.project.closed, a.project.closed:link, a.project.closed:visited { color: #999; }