A review is given of the present status of the theory ofsandpelectrons in deep traps. The theory of theFcenter in LiF is reviewed in detail including recent work on ionic displacements in the vicinity of the center. This is followed by a discussion of the work of Cohen and Heine and the general justification of the point ion approximation for the interaction of a trapped electron with a matrix composed of closed‐shell ions. Vacancies in diamond are discussed, and new results are reported for the three‐electron configuration of a vacancy in silicon. Trapped‐hole centers in the alkali halides are mentioned briefly.