Unlike the others, I'm not going to ignore your request and suggest you use another library. Instead, I'm going to point you back to markr's post and explain it a little better. The 'decorations' is basically the window style. The Win32 API's windows and Java's windows require you to set the window's style to make it borderless, and I'm guessing Xlib is no different. Check the headers (or documentation) on changing the window style, and you should find a solution.