The course begins with a discussion of many cryocooler applications followed by a study of thermodynamic and heat transfer fundamentals which are then used to explain how various types of gas-cycle cryocoolers achieve temperatures from about 2 K to 150 K. The operating principles and advantages/disadvantages of the three major recuperative cycles (Joule-Thomson Brayton and Claude) and the three major regenerative cycles (Stirling Gifford-McMahon and pulse tube) are explained. The course covers modeling design approaches fabrication techniques measurement methods and cycle comparisons. This year’s special topic of dilution refrigeration for millikelvin temperatures is given by Fons de Waele. After a general introduction he pays extra attention to dilution refrigerators that are precooled by pulse-tube refrigerators the so-called dry dilution refrigerators.