Page Inheritance In ASP.NET
http://www.codeproject.com/aspnet/AspNetInheritance.asp

Davis, Jon
Code Project, The
2004

Abstract:

Use object inheritance with System.Web.UI.Page to apply a common paradigm for user authentication, and extending the base web form feature set in your web application. Apply common security, specify per-page user access levels, and enforce common functionality, with only one line of code per page.