I am having a similar issue. The MDI children are form derived and I need to identifiy which window has the focus. I'm using this.MdiParent.ActiveMdiChild to derive the information, but what information in the object will determine this? The only thing, in my application, that seems to differentiate between the windows is the different WindowText that I assign for each child. And with that, I can't seem to access the text string as I get an error that says the information is protected. I am relatively new to Windows programming, so excuse me if I sound a bit naive.