An autocollimator is an optical instrument which uses its own collimated light to detect small angular displacements of a mirror. Electronic autocollimators provide a continuous output voltage, the sign and amplitude of which are proportional to the mirror displacement. Design and performance considerations of electronic autocollimators are discussed with emphasis on internal and external noise, the trade-off between bandwidth and sensitivity, selection of light sources, and uses. Included is a review of the different types of autocollimators and the criteria for selection of accessories.