This book meets the need for a clear and unified introduction to the physics of matter at low temperatures. It is particularly suitable for advanced undergraduate and postgraduate students, but will also be useful for researchers newly entering this field. The authors discuss the diverse phenomena that occur at low temperatures, some of which have no analogue in the everyday world at room temperature, and indicate the fundamental significance that many of them carry for basic physics. They explain the general principles involved in the design and use of low temperature systems, and how experimental measurements can be achieved in practice. The final chapter presents a brief account of the more important applications of low temperatures that are now being realized. There is a bibliography at the end of each chapter. Contents: Introduction, Solids: structure and phonons. Solids: electronic properties. Superconductivity. Helium·4. Helium·3. Obtaining low temperatures. Applications.