One appealing feature of string theory is that it provides a theory of quantum gravity. Gravity and Strings is a self-contained, pedagogical exposition of this theory, its foundations, and its basic results. In Part I, the foundations, are traced back to the very early special-relativistic field theories of gravity, showing how such theories, associated to the graviton concept, lead to general relativity. Gauge theories of gravity are then discussed and used to introduce supergravity theories. Part II covers some of the most interesting solutions of general relativity and its generalizations. These include Schwarzschild and Reissner-Nordström black holes, the Taub-NUT solution, gravitational instantons, and gravitational waves. Kaluza-Klein theories and the uses of residual supersymmetries are discussed in detail. Part III presents string theory from the effective-action point of view, using the results found earlier in the book as background. The supergravity theories associated with superstrings and M-theory are thoroughly studied, and used to describe dualitics and classical solutions related to non-pertubative states of these theories. A brief account of extreme black-hole entropy calculations is also given. This unique book will be useful as a reference book for graduate students and researchers, as well as a complementary textbook for courses on gravity, supergravity, and string theory.