Cryopumping involves the condensation and solidification of gas onto cryogenically cooled array surfaces. Control of the formation of the frost layers within the pump can improve its performance from both a vacuum and a capacity viewpoint. Vacuum performance of a cryopump involves the consistent attainment of required pressure levels within process allotted time constraints. Cryopump capacity involves the achievement of requisite vacuum levels for extended periods of time before regeneration is required. This article summarizes developments in the understanding of frost layer formation and its influence on cryopump vacuum performance and capacity. (C) 2010 American Vacuum Society. [DOI: 10.1116/1.3275748]