Sensing is the mechanism by which robots receive information from the world around them. Robot sensing, and in particular, robot vision is the basis for providing sensory inputs to a smart robot. Devices that make robot vision possible are typically classified as electro-optical sensors. Thus a critical review of robot vision is essentially a review of current and predicted capabilities for imaging electro-optical sensors. The critical element in an electro-optical sensor is the detector and most detectors are semiconductor devices. Thus we conclude that robot vision is closely tied to the state of the art in the development of photosensitive semiconductor materials and in the fabrication of large scale arrays of detector elements. This paper begins with a review of the fundamental principles that are important to electro-optical sensors. It then presents a brief tutorial on parameters for quantitatively evaluating the performance of detectors and electro-optical sensors. Selected state of the art sensor systems are next analyzed to show expected performance. Finally a review is given of detector technology as related to robot vision including a comparison of materials, array sizes, performance and cost.