Paul Cornell

Microsoft Silverlight is a cross-browser, cross-platform implementation of the .NET Framework for building and delivering the next generation of media experiences and rich interactive applications (RIA) for the Web.

Silverlight offers the following features:

• It runs in all popular Web browsers, including Microsoft Internet Explorer, Mozilla Firefox, and Apple Safari, and on Microsoft Windows and Apple Mac OS X.
• It is supported by a very small download that installs in seconds.
• It streams video and audio. It scales video quality to everything from mobile devices to desktop browsers to 720p HDTV video modes.
• It includes compelling graphics that users can manipulate directly in the browser.
• WPF and XAML. Silverlight includes a subset of the Windows Presentation Foundation (WPF) technology, which greatly extends the elements in the browser for creating UI, extending browser-based UI beyond what is available with HTML alone. Extensible Application Markup Language (XAML) provides a declarative markup syntax for creating elements.
• Extensions to JavaScript. Silverlight provides extensions to the universal browser scripting language that provide control over the browser UI.
• Integration with existing applications. Silverlight integrates seamlessly with your existing JavaScript and ASP.NET AJAX code to complement functionality you have already created. 
• Access to the .NET Framework programming model and to associated tools. You can create Silverlight-based applications using dynamic languages such as IronPython as well as languages such as C# and Visual Basic. You can use development tools such as Visual Studio to create Silverlight-based applications.
• Networking support. Silverlight includes support for HTTP over TCP. You can connect to WCF, SOAP, or ASP.NET AJAX services and receive XML, JSON, or RSS data.
• LINQ. Silverlight includes language-integrated query (LINQ), which enables you to program data access using intuitive native syntax and strongly typed objects in .NET Framework languages.

Got more time? Learn more:

• Silverlight Roadmap: http://msdn.microsoft.com/en-us/library/bb404708(VS.96).aspx
• Walkthrough: Creating Your First Silverlight Application: http://msdn.microsoft.com/en-us/library/cc838218(VS.96).aspx