The material in this chapter is provided as an introduction to those aspects of optics which play an important role in the subject of optical radiation safety. It is not intended as a comprehensive discourse but is simplified for those individuals who have responsibilities for safety of laser equipment and high intensity light sources, yet have not had rigorous training in optical physics. It may be conveniently bypassed by those familiar with optics, although it may serve as a useful introductory or refresher presentation of the subject for the individual who has not recently worked in optics or optical engineering.