A reissue of a classic book, corrected, edited, and typeset, to be published in the Biological Physics Series. Intended for undergraduate courses in biophysics, biological physics, physiology, medical physics, and biomedical engineering, this book is an introduction to statistical physics with examples and problems from the medical and biological sciences. Topics include the elements of the theory of probability, Poisson statistics, thermal equilibrium, entropy and free energy, and the second law of thermodynamics. Chapters include problems and references. The book can be used as a supplement to standard introductory physics courses, and as a text for medical schools, medical physics courses, and biology departments. The three volumes combined present all the major topics in physics. Originally published in 1974 from the authors's typescript, this reissue will be edited, corrected, typeset, the art redrawn, and an index added. These books are being reissued by Springer in the Biological Physics Series in response to frequent requests to provide these texts to satisfy the growing need among students and practitioners in the medical and biological sciences with a working knowledge of the physical sciences. The books are also in demand in physics departments either as supplements to traditional intro texts or as main text for those departments offering courses with biological or medical physics orientation. A solutions manual will be available. The authors are recognized experts in the field, and are under contract for an upperlevel/grad text in biological physics. Benedeck was the recepient of the 1995 Irving Lanmuir Prize from the American Physical Society for Chemical Physics, and the 1994 Biological Physics Prize by the American Physical Society.