Small autonomous robots require fast, compact, and low-power sensors for processing visual signals and safely navigating in their environment. We present a custom VLSI vision sensor with these characteristics that provides information on the scene contrast, local motion, and position of salient targets. The Tracker Motion Sensor (TMS) is a mixed signal vision system with focal-plane continuous time processing circuits that computes spatial and temporal derivatives for performing edge detection, and for measuring their velocity and direction. In addition, the TMS contains analog circuits that implement a model of selective attention that reports the position of visual targets in order of decreasing saliency. We describe the main circuit blocks and present measurements from the fabricated chip to show how it is an ideal sensor for robotic applications that must select and track moving targets.