Cross platform mobile development is the holy grail of development right now. In this talk we'll examine strategies and patterns for maximizing code re-use when building native cross-platform mobile applications in C# with Xamarin that reuse back end code while still using platform-specific UX and taking advantage of platform-specific features. We'll examine different code sharing technologies including Portable Library Projects, Compiler Directives, and architectural positioning. We'll also review cross platform libraries, methodologies, and get guidance directly from the source: a Xamarin team member.