diff --git a/CHANGELOG.md b/CHANGELOG.md
index 5ada5559..b4ebf695 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -17,10 +17,12 @@ Release date: TBD
 
 #### Windows
 - Update Mattermost icon for desktop notifications in Windows 10.
+- An existing application instance will be reused instead of starting another instance.
 
 #### Linux (Beta)
 - Added an option to make the taskbar icon flash on new messages
 - Added the badge to count mentions for Unity.
+- An existing application instance will be reused instead of starting another instance.
 
 #### OS X
 - Added an option to toggle the red dot icon for unread messages (default is on).
@@ -31,7 +33,6 @@ Release date: TBD
 
 ### Bug Fixes
 
-
 ## Release v1.3.0
 
 Release date: 2016-07-18
diff --git a/src/main.js b/src/main.js
index df4433ac..9a3b5c52 100644
--- a/src/main.js
+++ b/src/main.js
@@ -128,6 +128,17 @@ const trayImages = function() {
 }();
 var willAppQuit = false;
 
+// If there is already an instance, activate the window in the existing instace and quit this one
+if (app.makeSingleInstance((commandLine, workingDirectory) => {
+    // Someone tried to run a second instance, we should focus our window.
+    if (mainWindow) {
+      if (mainWindow.isMinimized()) mainWindow.restore();
+      else mainWindow.show();
+    }
+  })) {
+  app.quit()
+}
+
 function shouldShowTrayIcon() {
   if (process.platform === 'win32') {
     return true;
diff --git a/test/specs/app_test.js b/test/specs/app_test.js
index a9660578..261bd896 100644
--- a/test/specs/app_test.js
+++ b/test/specs/app_test.js
@@ -61,4 +61,21 @@ describe('application', function() {
       config.version.should.equal(settings.version);
     });
   });
+
+  it('should be stopped when the app instance already exists', function(done) {
+    this.app.start().then(() => {
+      const secondApp = env.getSpectronApp();
+      secondApp.start().then(() => {
+        clearTimeout(timer);
+        return secondApp.stop();
+      }).then(() => {
+        done(new Error('Second app instance exists'));
+      });
+      // In the correct case, 'start().then' is not called.
+      // So need to use setTimeout in order to finish this test.
+      const timer = setTimeout(() => {
+        done();
+      }, 3000);
+    });
+  });
 });