Silverlight is a new cross-browser, cross-platform execution of the .NET Framework for building and delivering the subsequent generation of media experiences and Rich Interactive Applications (RIA) for the web. It executes in all popular browsers, including Microsoft Internet Explorer, Mozilla Firefox, Apple Safari, Opera. The plug-in essential to run Silverlight is very small in size therefore gets installed very fast. It is combination of dissimilar technologies into a particular development platform that allows you to choose tools and the programming language you wish to use. Silverlight integrates seamlessly with your existing JavaScript and ASP.NET AJAX code to complement functionality which you have already created.

Silverlight aims to compete with Adobe Flash and the presentation components of Ajax. It moreover competes with Sun Microsystems' JavaFX, which was launched a few days after Silverlight.

There are 2 versions of silverlight:

Silverlight 1.0:
Silverlight 1.0 consists of the core presentation framework, which is liable for UI, interactivity and user input, necessary UI controls, graphics and animation, media playback, DRM support, and DOM integration.

Silverlight 1.1:
Silverlight 1.1 includes a version of the .NET Framework, with the full universal Language Runtime as .NET Framework 3.0; so it can carry out any .NET language including VB.NET and C# code. Unlike the CLR included with .NET Framework, many instances of the CoreCLR included in Silverlight can be hosted in one process.[16] With this, the XAML plan markup file (.xaml file) can be increased by code-behind code, written in any .NET language, which contains the programming logic.

Benefits of Microsoft Silverlight:

Microsoft Silverlight mostly attracts developers who are well familiar with .NET. The developer will have to learn Flash and Flex from scratch. His in-depth understanding of .NET is an added advantage and can start using Silverlight straight on.

Microsoft Silverlight is easy to understand unlike other frameworks used to build rich Internet applications. The Web developers that are working with AJAX or Flex or other frameworks used for creating rich Internet applications may be necessary to learn this technology. Microsoft Silverlight addresses the cost of formation and rich media delivery in a many ways which include; providing a methodical set of tools for building and design teams and reasonable delivery of audio and video experiences while using Windows Media Streaming.