Gravitational lensing, previously thought of as just a curiosity associated with the bending of light predicted by General Relativity, has been gaining more attention in recent years for what it can tell astronomers and cosmologists about the geometry of the universe, its expansion rate and matter content, the formation and distribution of large scale structures, and the nature of dark matter. It may also provide the ability to look for non-luminous stellar objects (black holes, neutron stars, etc.). Mollerach and Roulet (both of the Centro At=mico Bariloche, Argentina) provide a pedagogical presentation of the various aspects of lensing appropriate for students at a graduate level. After a brief historical introduction, chapters cover the bending of light, lensing theory, macrolensing results, and microlensing. Annotation c. Book News, Inc., Portland, OR (booknews.com)