With ASP.NET Web Form, you typically use the [Model View Presenter pattern](http://msdn.microsoft.com/en-us/magazine/cc188690.aspx). 

GlenH7 mentioned in [his answer](https://softwareengineering.stackexchange.com/a/155011/173647) MVVM; while it is an elegant pattern, ASPX Webform just doesn't have great support for that. MVVM is more popular in the WPF world.