We present a binocular active vision system that can attend to and xate a moving target. Our system has an open and expandable design and it forms the rst steps of a long term e ort towards developing an active observer using vision to interact with the environment, in particular capable of gure-ground segmentation. We also present partial real-time implementationsof this system and show their performance in real-world situations together with motor control. In pursuit we particularly focus on occlusions of other, both stationary and moving, targets, and integrate three cues to obtain an overall robust behavior, ego-motion, target motion and target disparity. We argue that an active vision system must be open, expandable, and operate with whatever data are available momentarily. The integration of many cues and concurrent modules, rather than sophisticated recovery mechanisms, forms a pervading theme. We stress that anactive systemmustbe equipped withmeansandclues to changeits attenti...