This textbook is intended for introductory courses in physics, engineering and chemistry at universities, polytechnics and technical colleges. It provides either an elementary treatment of thermal physics, complete in itself, for those who need to carry the subject no further, or a sound foundation for further study in more specialised courses. The author gives a clear and concise account of those basic concepts that provide the foundations for an understanding of the thermal properties of matter. The area covered corresponds very roughly to the traditional topics of heat, kinetic theory, and those properties of matter for which there are elementary explanations in terms of interatomic forces. The book is not concerned with experimental detail but with ideas and concepts, and their quantitative application through simple models. The author provides many problems for which the answers are included. The book should also be useful in teacher training and as a reference book in the libraries of schools where pupils are being prepared for tertiary courses.