This document introduces XAML, WPF, Silverlight, and Windows Phone. It discusses that XAML is an XML-based language used across these Microsoft technologies to define user interfaces. WPF uses XAML and GPU processing to improve performance. Silverlight evolved from a streaming platform to a full programming language and is used to build rich internet applications. Windows Phone uses the Silverlight runtime and tooling. All three technologies follow the MVVM architectural pattern to separate the user interface from business logic and data bindings.