If you don't know how each ASP.NET request is processed then you are lacking a vital piece of knowledge. The HttpApplication is usually un-heard of and it works quietly behind the scenes - well not really. If you have written a HttpHandler or HttpModule or any application with some sort of complexity before - you probably already know what its all about. The HttpApplication is the base class for all ASP.NET application objects, therefore, an HttpApplication class is created for each request.