Prior to the availability of high-energy electron accelerators, photon activation analysis was limited to the determination of deuterium and beryllium with isotopic gamma-ray sources. During the past 15 years, however, the development of high-current cyclic and linear electron accelerators has made possible many analyses not readily accomplished by other methods. These include the determination of carbon, nitrogen, and oxygen at levels well bellow 1 micron g. This review discusses the determination of beryllium and deuterium with isotope sources; accelerator-produced photons and nuclear considerations in photon activation analysis; the determination of carbon, nitrogen, and oxygen; the determination of heavier elements, with emphasis on biological, geochemical, oceanographic, and forensic matrices; and errors and corrections in photon activation analysis.