ASP.NET Page Life Cycle Overview

"When an ASP.NET page runs, the page goes through a life cycle in which it performs a series of processing steps. These include initialization, instantiating controls, restoring and maintaining state, running event handler code, and rendering. It is important for you to understand the page life cycle so that you can write code at the appropriate life-cycle stage for the effect you intend."

http://msdn.microsoft.com/en-us/library/ms178472.aspx