A while back I wrote a post describing how the DetailsView, GridView, UpdatePanel and the AjaxControlToolkit's ModalPopup controls could be used to implement the common Master/Details UI pattern. I cheated a bit when creating my original example in that I didn't really complete the implementation - the Save button on the popup didn't actually do anything. Since writing that post I have received a lot of email and a number of people left comments asking me to complete the example - so here it is. If you plan on reading through this article, I recommend playing around with the demo site to get a feel for how the page works. All data changes are only persisted to memory, so don't worry about messing up the data set.