Silverlight runs C# and Visual Basic code, and so it seems natural that a business application might share some code between the Silverlight client and its ASP.NET Web server. You may want to run some code client-side for interactivity, but re-run that code on the server for security or reliability. This is possible, and there are several techniques you can use to accomplish this goal. Learn about the various techniques and their pros and cons. Some techniques work better in C#, others in VB. Still others are simpler with a little extra tooling or code-generation. Any serious Silverlight business application will almost certainly face this issue, and this session gets you going fast!