Gill Cleeren wrote this nice article on Styles and Triggers in WPF

"Windows Presentation Foundation, or WPF, previously known by its code-name “Avalon”, is an all-new presentation framework included in Windows Vista. WPF is also available for Windows XP SP2 and Windows Server 2003 SP1 as part of the .NET Framework 3.0. WPF consists of numerous new technologies that as a whole provide a unified programming model for applications that will run standalone or inside a browser. In this article, we will focus on the aspect of styles and triggers.

Styles make it possible to create applications with a uniform look and with a high level of maintainability. Triggers allow WPF styles to change one or more properties in response of a user interaction. In this document, we will use both these technologies to create a richer user experience."

Link