Extreme ASP.NET: Codebehind and Compilation in ASP.NET 2.0 -- MSDN Magazine, January 2006 (This is a very good article that clears the compilation model in .Net 2.0). In the final release of windows forms and in the initial release of ASp.NET 2.0 the codebehind partial class and the parsed .aspx class is merged together into one class at runtime and because of some inflexibility (explained in detail in the article) now its modified to a new model in ASp.NET 2.0 so that the partial code behind class is merged with another partial class (that contains all the control declarations) and combined into a single class, the parsed aspx is built into a class that inherits from the previously merged class.