XAML, Extensible Application Markup Language, is Microsoft's XML-based language for creating a rich GUI, or graphical user interface. XAML supports both vector and bitmap types of graphics, as well as rich text and multimedia files. XAML was introduced in 2003 as the language behind the Windows Presentation Foundation, which is Microsoft's GUI design tool for the upcoming Windows Vista operating system.
XAML files can be produced in either Visual Studio, Microsoft's development tool for the .NET Framework, or in Microsoft's Expression toolset for designers, before exporting them to the Windows Presentation Foundation. This allows designers, who focus on the front end of an application, and developers, who focus on the code that defines the front end, to work from the same code base, which improves productivity.