Human semen analysis is the first biological step of male fertility assessment. Its performance requires the use of standardized and objective procedures. The results of the tests may allow to conclude to a man's sterility when they reveal e.g. an azoospermia or an alteration of sperm morphology or motility incompatible with fertilization. More often however, it is difficult to precisely determine the relationships between the observed sperm anomalies and infertility. In a follow-up study of 520 infertile men over 3 years, the pregnancy rate was found to be significantly lower only in the cases where sperm concentration values were less than 5.10(6)/ml and unchanged for concentrations above this value. No threshold values were found for sperm motility and morphology, although the chances of conception were closely related to these two parameters for sperm concentration values above 5.10(6)/ml. Various tests have been described to evaluate the human sperm ability to migrate through the female genital tract and fertilize the oocyte. These tests and the human in vitro fertilization assay allow a better understanding of the structural and dynamical parameters mostly involved in sperm function.