"A common problem when developing an n-tier RIA solution is coordinating application logic between the middle tier and the presentation tier. To create the best user experience, you want your RIA client to be aware of the application logic that resides on the server, but you do not want to develop and maintain the application logic on both the presentation tier and the middle tier. RIA Services solves this problem by providing framework components, tools, and services that make the application logic on the server available to the RIA client without having to manually duplicate that programming logic." · http://msdn.microsoft.com/en-us/library/ee707344(VS.91).aspx