This chapter focuses on various cryoprotectants and their application in preserving gametes and embryos. Penetrating cryoprotectants provide buffering against salt-induced stress by acting as solvent, reducing the solute concentration in the remaining water fraction inside the cell until the system is cooled to a low enough temperature. Various penetrating cryoprotectants have been used successfully in in vitro fertilization (IVF) to preserve sperm, embryos, and oocytes. Non-penetrating cryoprotectants are often included in media used for warming/thawing of cells to avoid osmotic shock. Most toxicity concerns exist with penetrating cryoprotectants rather than the non-penetrating cryoprotectants. In regard to reproductive biology and assessing suitability/toxicity of a cryoprotective agent, certain endpoint measures are commonly assessed. Cryoprotectants serve to prevent damage induced by the cooling/freezing process, in part by reducing ice crystal formation and by reducing stress resulting from osmotic shock.