Radiation-induced apoptosis has been a topic of intense research during the last decade. Its recognition as a significant component of radiation-induced cell death has initiated several lines of investigation aimed at modulating the apoptotic response and thereby radiosensitivity. These strategies require the integration of both classical radiobiological concepts and the knowledge of the biochemical and molecular biological mechanisms involved in apoptosis induction. This review discusses mechanisms of radiation-induced apoptosis and highlights the radiobiological and radiotherapeutical relevance of this mode of cell death.