For common computer interaction the mouse is established as a standard device. The recognition of freehand 3D-interaction has already been implemented by detecting the fingertips and the eyes of the users. This application is based on the stereo-photogrammetry approach with two webcams. Attempts with a single webcam have been performed as well to quit the synchronisation of two video streams. Using the range-imaging technology the user can move in front of the display from 30 cm up to the maximal ranging distance that is supported by the camera. The body, especially head and hand, can be detected in 3D within the operating range and an additional gesture-analysis tool is able to interpret the commands of the user. With this approach, the computer mouse is not needed anymore. The main topic of this paper is the multi-user interaction. Operating the computer at the same time with several users is not supported by the actual operating systems. The simultaneous detection of several users and their hands in 3D was achieved. A fast switching between the users to control the computer in turns is explained.