Cryopumping has come to the forefront as the fastest growing high vacuum pumping mechanism. With the major advantages of cryopumping, however, also comes the necessity of addressing the specifics of its operation to ensure optimum performance. One of the most overemphasized and misunderstood aspects of the cryopump has been regeneration. Even after years of usage, for many users, regeneration is still mysterious. This article explains the process of regeneration and answers the question of why, when, and how to regenerate a cryopump.