A review of optical range sensing techniques for machine vision is given. Four basic categories of range sensing techniques are discussed: geometric techniques, time-of-flight techniques, interferometric techniques, and diffraction techniques. The basic principles are elucidated, and general comparisons are made between the groups. Representative examples are given of many different approaches. The challenge for optics and optical computing is to develop new range sensors that are fast and accurate and require little or no post-detection processing.