Computer users switch between applications and windows all day, but finding the target window can be difficult, particularly when the total number of windows is high. We describe the design and evaluation of a new window switcher called SCOTZ (for Spatially Consistent Thumbnail Zones). SCOTZ is a window switching interface which shows all windows grouped by application and allocates more space to the most frequently revisited applications. The two key design principles of SCOTZ are (1) predictability of window locations, and (2) improved accessibility of recently and frequently used windows. We describe the design and features of SCOTZ, and present the findings from qualitative and empirical studies which demonstrate that SCOTZ yields performance and preference benefits over existing window switching tools.