Wouldn’t it be nice to develop a mobile App with C# and Visual Studio that runs on Android, iOS and WP8? Additionally with native Look & Feel and platform-specific features for a familiar user experience? This is possible with the Xamarin tool chain. It is based on Mono, an open .Net implementation according to the ECMA standard for C#. This presentation will show how an App with a cross-platform architecture can be developed. Using common engineering practices (like TDD, CI, etc.), we also discuss our experience from several projects. We use a demo application which runs on Android, iPhone and Windows, and has been implemented to a large extent with the MvvmCross framework.