Cryopreservation (freezing at super cold temperatures) of tissue and cells is a technique which puts the cells in suspended animation where they can retain their viability indefinitely. Cryopreservation protects against catastrophic losses caused by such events as disease outbreaks, fire, breeding cessation, or genetic contamination and eliminates the necessity of maintaining stocks 'on the shelf' when those stocks are not being actively used. Cryobiology improved rapidly with the discovery of the beneficial effects of cryoprotectant substances that are added to cell freezing solutions. Cryopreservation is now routinely used to store semen, embryos and all types of cells/tissue of animals and humans.