Abnormal spermatozoa have been historically associated with male subfertility and sterility. As early as 1927, an insightful report by Williams and Savage in the Cornell Vet stated that "the dimensions of sperm heads from good fertility bulls are remarkably uniform". This is still true. Presence of abnormal spermatozoa in semen is one of our most sensitive indications that spermatogenesis of a male has been impaired. In addition, occurrence of certain types of abnormal sperm are more dangerous, and can indicate that normal-appearing sperm in the same sample may also be abnormal or incompetent in fertilization or sustaining embryogenesis once initiated. In this paper, we will summarize current concepts of how sperm morphology impacts fertilization rate, as well as early embryogenesis, by examining their transport in the female and engagement of the ovum. Also discussed is the relationship of sperm morphology as we measure it in the breeding soundness exam to what we recognize as the two main components comprising seminal deficiencies in artificial insemination: 1) those deficiencies which can be overcome by raising the sperm dosage to the female (compensable) 2) and those deficiencies where subfertility exists regardless of sperm dosage (uncompensable).