In this paper we present importance-driven compositing window management, which considers windows not only as basic rectangular shapes but also integrates the importance of the windows' content using a bottom-up visual attention model. Based on this information, importance-driven compositing optimizes the spatial window layout for maximum visibility and interactivity of occluded content in combination with see-through windows. We employ this technique for emerging window manager functions to minimize information overlap caused by popping up windows or floating toolbars and to improve the access to occluded window content. An initial user study indicates that our technique provides a more effective and satisfactory access to occluded information than the well-adopted Alt+Tab window switching technique and see-through windows without optimized spatial layout.