This document discusses cross-platform development between Windows 8 and Windows Phone 8. It outlines common APIs, structures, and strategies that can be used to build apps for both platforms, including portable class libraries, MVVM, and conditional compilation. Specifically, it shows how abstraction layers like ViewModels, shared base class libraries, and extension methods allow code to be reused while still supporting each platform's native controls and user experience conventions. The goal is to allow developers to build high quality, synchronized experiences across devices while accounting for differences in capabilities and form factors.