Specifying an electronic autocollimator for optimum performance in a given application involves an often bewildering choice of performance trade-offs. This paper, intended to be primarily tutorial, will proceed from a brief description of the operating principles and advantages of electronic autocollimators to a discourse on performance specifications and trade-offs. Primary specifications are sensitivity, data bandwidth, angular measuring range, acquire range, and mirror distance. Secondary specifications include size, objective lens focal length, weight, materials, and vacuum or space rating. The trade-offs between specifications, arising from the requirements or constraints imposed by the applications, will determine the ultimate performance of the autocollimator.