We present a robust framework for tracking skeleton joints in real-time by using a single time-of-flight depth sensor. The framework is able to remove the background noise inherent in time-of-flight cameras, detect multiple people, and track up to 30 joints of free motion for each person. The approach has several advantages over traditional motion capture, as it is a cheap alternative to magnetic and optical systems, and requires no markers whatsoever. Unlike markerless systems based on RGB cameras [Duetscher et al. 2000; Kehl and Van Gool 2006], our framework yields dependable results at an interactive rate using a single camera.