This book is for those physicists, physical chemists, metallurgists and engineers who need to carry out investigations at low temperatures. It deals with the production and measurement of low temperatures, the handling of liquefied gases on the laboratory scale, and the principles and details of the design of experimental cryostats, including the problems of heat transfer and temperature control. While covering the technical details needed by professional researchers, such as the electrical and thermal conductivities of materials used in making low temperature equipment, the book includes enough explanations of the fundamental principles that it will also be useful to advanced university students.