This textbook gives a clear account of the manner in which knowledge in many branches of physics, such as gravitation, thermodynamics, atomic physics, and nuclear physics, can be combined to gain an understanding of the structure and evolution of stars. A major aim is to present the subject as one in which advances are still being made. The first half is an account of the observational properties of stars and a discussion of the equations that govern their structure. The second part discusses recent theoretical work on stellar evolution. The successes of the theory are stressed, but attention is also drawn to phenomena that are not completely understood. This is a new edition of a widely-used textbook first published in 1970. New topics include mass loss from stars and close binary stars.