Silverlight is Microsoft's new browser-based plug-in for delivering richer interactive applications to users over the web. Silverlight 2 is Microsoft's second release of the Silverlight platform. Silverlight 2's biggest change from Silverlight 1.0 is the inclusion of a compact version of the .NET Framework, complete with the .NET Framework 3.0 Common Language Runtime. By adding .NET to Silverlight, Microsoft makes it easy for .NET developers to reuse their existing programming skills, collaborate with designers, and quickly create rich applications for the Web.
Still, one of the key benefits of Silverlight 2 is that it can execute any .NET language, including C# and VB.NET. Unlike the CLR included with the "normal" .NET Framework, multiple instances of the core "Silverlight CLR" can be hosted in a single process. With this, the layout markup in the Silverlight XAML file (.xaml file) can be augmented by code-behind code with all programming logic written in any .NET language.
Silverlight 2 ships with a "lightweight" version of the full .NET Framework, which features, among other classes, extensible controls, XML Web Services, networking components, and LINQ APIs. This class library is a subset of (and is considerably smaller than) the .NET Framework's Base Class Library, which enables the Silverlight plug-in to be a fast and small download. For security, all Silverlight code runs in a sandbox environment that prevents invoking platform APIs, protecting user computers from malicious code. Silverlight 2 also adds support for DRM in media files, a fact that will make some people happy and others cringe.