Increasingly, the cryopreservation of living cells is being attempted by researchers whose primary interest and experience is with the medical applications of those cells or tissues and whose prior experience with cryobiology may be negligible. It is therefore generally necessary to imitate some regimen used by others, perhaps with some other cell type and attempt to optimize the recovery empirically. This article makes no attempt to provide specific protocols for the many individual cell types. Rather it is a primer that may help to give such investigators an insight into the basic principles of cell freezing, cryoprotectants, and, particularly, their addition and removal. Finally, the article summarizes the five different approaches to applied cryopreservation: ultrarapid freezing and thawing, controlled-rate freezing, freezing with nonpenetrating polymers, vitrification, and equilibrium freezing.