In recent years, impressive progress has been made in the biochemical and molecular characterization of both the spermatozoon and the oocyte. The use of animal models with genetic mutations or "knocked-out" genes has enhanced our understanding of the growth, development and function of the male and female gamete. Significant progress also has been made in elucidating the cellular and molecular basis of the sperm-egg interaction leading to fertilization. These recent findings will hopefully enable the development of both more appropriate treatment strategies for overcoming infertility and novel contraceptives.