Web Part Extenders are a different type of web parts, which instead of rendering data or HTML markup, provide an extended functionality or behavior to one or more existing web parts on a web part page. They can be used in both SharePoint and ASP.NET sites. Until now a common way of extending the functionality of existing web parts was to either write a new web part from scratch or subclass from an existing web part. This approach however requires advanced programming and access to the web part code being extended or modified. Web Part Extenders allow SharePoint and ASP.NET component developers to add functionality to one or more web parts using the loosely coupled interfaces. End users can use these building blocks to enhance the web application user experience.