WPF started as a Windows desktop technology focused on 2D and 3D graphics, controls, layout, styles and data binding using XAML. Over time it added features like animation, templates, commands and integrated better with Windows. Silverlight launched as a browser plugin with a lightweight version of the WPF runtime and tooling. It grew to support additional media, graphics and interactivity. Development tools for both WPF and Silverlight expanded in Visual Studio and Expression Blend.