**1. Introduction**

20 Will-be-set-by-IN-TECH

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The numerous effects that cryopreservation can induce in spermatozoa, ranging from lethal injuries to those which merely impair their subsequent function. In the last few years, the considerable increase in our understanding of both, the cell physiology of spermatozoa, and the stress of cryopreservation, have contributed to a renewed interest in improving the performance of cryopreserved semen.

Despite the significant progress, the post-thaw viability and fertility of the cryopreserved sperm are still reduced, as a consequence of accumulated cellular injuries that arise throughout the cryopreservation process. Many laboratory tests have already been carried out to verify these detrimental effects and their origin. Their is needed to well understand the whole process of cryopreservation and its influence on sperm function. As a consequence, it would lead to a subsequent improvement of sperm viability by means of reformulated protocols and approaches helping to minimize the detrimental effect of cryopreservation.

Here, we present an overview of the cryopreserved semen assessment methods in the light of sperm physiology, in order to relate these factors to altered functions of cryopreserved sperm and to determine the fertilizing potential of the frozen-thawed semen.
