Until about 20 years ago, sperm assessment in the laboratory was focused on motility, morphology and acrosomal integrity. Then came the gradual realisation that, because the main objective of a spermatozoon is to deliver an intact genetic payload of DNA to the egg, being able to check DNA quality of spermatozoa would be equally important, if not more so. Research over the last two decades has therefore led to the development of several techniques for reliably detecting DNA strand breaks, and the more recent focus has been directed towards understanding the fertility implications of DNA damage. It is now clear that evolutionary history has played an important role in determining the stability of sperm DNA under stressful conditions, and that the nature of the DNA-protein interactions also influence the extent to which fertility is affected by both technical procedures involved in sperm preservation and the basic biology of the species concerned. Here we present an overview of the principles involved in DNA assessment and also provide some cases studies that illustrate the influences of species diversity.