Extensible Application Markup Language，XAML，是WPF（Windows Presentation Foundation）的一部分，是一种XML的用户接口描述语言，有着HTML的外观，又揉合了XML语法的本质，例如：可以使用<Button>标签设置按钮（Button）。类似Linux平台下的glade。至于WinFX XAML Browser Application（XBAP）是用XAML作界面描述，在浏览器中运行的程序，可取代过去的ActiveX、Java Applet、Flash。

Extensible Application Markup Language (XAML, /ˈzæməl/) is a declarative XML-based language developed by Microsoft that is used for initializing structured values and objects. It is available under Microsoft's Open Specification Promise. The acronym originally stood for Extensible Avalon Markup Language - Avalon being the code-name for Windows Presentation Foundation (WPF).