...as an account of classical general relativity, this well produced and excellently translated book has many virtues. Physics Bulletin A nice introduction to the theory and practice of finding and using symmetries to solve differential equations. American Mathematical Monthly ...Stephani's book does a good job of motivating the study of Lie group methods for differential equations from an elementary standpoint. SIAM Reviews The author, who has an easy-to-read practical style, consistently keeps the emphasis on applications. Thus, most physicists will be able to get useful information about ordinary differential equations (ODE's) and partial differential equations (PDE's), without being bogged down in cumbersome mathematical formalism...well worth reading if one is at all interested in sophisticated and powerful symmetry techniques for handling differential equations and if one wishes to have the most straightforward approach to the topic. D. E. Vincent, Physics in Canada ...Stephani...has built a book that tries to guide its readers toward a sure knowledge of this very important tool for finding solutions of (nonlinear) differential equations. In the early sections, the derivations presented are the most clear and detailed ones that this writer has ever seen...Students new to this area will find reading or studying the current book an altogether enjoyable occupation, without any of the intimidation that sometimes is caused by similar books. J.D. Finley, Foundations of Physics