Each release of Silverlight it is the goal to make sure existing Silverlight applications continue to work. Since I think what this means causes some confusion Im going to do my best to explain what we mean by this. Silverlight 3 application working with Silverlight 4 Okay, scenario 1 is I have a Silverlight 3 application (XAP), will that still work as-is in Silverlight 4? Yes, this is the situation we refer to as backward compatibility. What this means is that existing compiled XAPs under previous...Did you know that DotNetSlackers also publishes .net articles written by top known .net Authors? We already have over 80 articles in several categories including Silverlight. Take a look: here.