Nuclear demagnetization for ultra-low temperatures

•We review the nuclear demagnetization refrigerator used in ultra low temperature experiments.•The basics principle, methods, and materials are described.•Superconducting heat switch and thermometers used in nuclear demagnetization are also presented.•We introduce our nuclear demagnetization cryostat, heat switch, and thermometers. Nuclear demagnetization is one of the most successful methods of cooling an appreciable amount of matter to the lowest temperatures. The principle of nuclear demagnetization is the same as that of the adiabatic demagnetization of a paramagnetic salt; however, there is a significant difference in practice. This article focuses on nuclear demagnetization refrigeration used in experiments at millikelvin and much lower temperatures. After a brief overview of the basic principle and methods, typical requirements of the refrigerants are described from the view point of experiments. The heat switch and thermometry used in nuclear demagnetization experiments are also discussed.