PopupControl is an ASP.NET AJAX extender that can be attached to any control to open a popup window that displays additional content. This popup window will probably be interactive and located within an ASP.NET AJAX UpdatePanel. So, it will perform complex server-based processing (including postbacks) without affecting the rest of the page. The popup window can contain any content including ASP.NET server controls, HTML elements, etc. Once work of the popup window is done, a simple server-side call dismisses it and triggers any relevant script on the client to run and update the page dynamically.