Few scientific issues arouse as much public controversy as the effects of radiation. This booklet is an attempt to summarize what is known about radiation and provide a basis for further discussion and debate. The first four chapters of the booklet are based on the most recent reports to the United Nations' General Assembly by the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR). These chapters deal with: (1) radiation and life; (2) natural sources of radiation; (3) human-made sources of radiation; and (4) the effects in humans of radiation. The final chapter is an attempt to discuss the issue of acceptability of risks from radiation, a subject not addressed in the UNSCEAR reports. (TW)