This paper presents a novel three-dimensional model-based tracking system which has been incorporated into a visual servoing system. The tracking system combines modern graphical rendering technology with constrained active contour tracking techniques to create wireframe-snakes. It operates in real time at video frame rate (25 Hz) and is based on an internal CAD model of the object to be tracked. This model is rendered using a binary space partition tree to perform hidden line removal and the visible features are identi ed on-line at each frame and are tracked in the video feed. The tracking system has been extended to incorporate real-time on-line calibrationand tracking of internal camera parameters. Results from on-line calibration and visual servoing experiments are presented.