Spermatozoa were the first cells to be cryopreserved over 50 years ago, following the serendipitous discovery of the cryoprotective compound glycerol. This pioneering work was followed by the introduction of a series of other cryoprotectant chemicals referred to collectively as cryoprotective agents. Glycerol has been widely used in the cryopreservation of bull and human spermatozoa, although results are still highly variable across species as well as among individuals within a species. Recently, significant information has been gained with regard to the fundamental cryobiology of several mammalian species' spermatozoa that can be used to reduce this variability and develop improved methods for cryopreservation. In this concise review, we will discuss the fundamental cryobiology of cells in general and of mammalian spermatozoa in particular.