.net 2005 uses a different compilation mode, called dynamic compilation. In .net2003, the compilation was handled by Visual Studio and the result was a dll in the bin folder. With .net2005, ASP.NET handles the compilation "on-the-fly" and therefore there is no dll. But there is a new add-in (now part of Visual Studio 2005 SP1) called Web Application Projects which allows you to use the same compilation mode used in .net2003; a dll is compiled by VS and placed in the bin folder. One major reason for the creation of this add-in was to assist in the upgrading of .net2003 projects to .net2005. http://ASP.NET has an article regarding the Web Application Projects on there home page.