This document discusses cross-platform mobile development using Xamarin and Visual Studio. Key points include: - Using C# and .NET with Xamarin allows building iOS, Android, and Windows Phone apps with one shared codebase while still getting native performance and user experience. - The code compiles to native for each platform, rather than being interpreted, and full access to platform SDKs is provided. Shared code, data layers, and platform abstractions allow code reuse. - Visual Studio solutions can contain projects for shared code, platform-specific code for each mobile OS, and tests. Linking or portable class libraries are recommended for sharing code. - Considerations include designing native U