Long-term storage of cell stocks insures that cells are available for use whenever needed. Cryopreservation of cells is the method of choice for preservation of important or rare cell stocks. There are several factors to consider when establishing a protocol for freezing, thawing, and recovery of cells after storage. These parameters may include cell concentration, cryoprotectant choice and concentration, and thawing rate among others. Further, the assessment of cell viability and/or function prior to and following cryopreservation is imperative in order to accurately determine downstream utility as well for optimizing the cryopreservation process. This chapter is designed to provide guidance and insight into developing robust and successful protocols for preserving cells that will preserve cell stocks and provide optimal cell yield and viability.