I assume that you want to get the window handle from a thread id. To do that, I would: Pass the thread id to GetProcessIdOfThread() to obtain a process id Because a process can open multiple windows, you need to return a collection. Iterate every window, getting their process ids. If it matches the id from 1., then add the window handle to the collection OSDev :)

Have a look at this article: Detect if another process is running and bring it to the foreground[^] daxfrost There Are 10 Kinds Of People, Those That Understand Binary, And Those That Don't