One of a series of general interest publications on science topics, this booklet provides a non-technical introduction to the subject of volcanoes. Separate sections examine the nature and workings of volcanoes, types of volcanoes, volcanic geological structures such as plugs and maars, types of eruptions, volcanic-related activity such as geysers and hot springs, world volcanic regions, plate tectonics theory, extraterrestrial volcanic activity, techniques of research and monitoring, and the human and economic repercussions of volcanic eruptions. The text is accompanied by numerous photographs illustrating the various types of volcanic activity and diagrams clarifying internal processes involved in volcano formation and eruption. (LP)