**2.1 History of human spermatozoa cryopreservation**

Remarkably, the first reference of empirical sperm freezing dates as far back as the late 16th century, but it was only with the discovery in 1937 by Bernstein and Petropavlovski that glycerol can aid spermatozoa in surviving long term freezing, that sperm cryopreservation became practical. Expansion of artificial insemination for the dairy industry led to further important research in the field of cryobiology (E. Isachenko, 2003, as sited in Bernstein & Petropavlovski, Polge et al., 1949). Shortly after these practices were initiated with animals, the first pregnancies were reported in humans after insemination with frozen spermatozoa. The next milestone was the discovery of the possibility to store human spermatozoa in LN2 at -196°C, resulting in superior recovery rates compared to storage at higher temperatures between -20 and -75°C. After the era of empirical freezing; cryobiology matured to its fundamental stage, focusing on the biophysical and biochemical principals of cryopreservation, further advancing the field (Mazur et al., 1972. A comprehensive review of the historical background of sperm freezing was recently published and is recommended for readers looking for more details (Katkov et al., 2006).
