Complete functional oocyte maturation involves many complex processes that occur within preovulatory follicles and are initiated and sustained by the gonadotropins, steroid hormones and many recognized and unrecognized factors. The product of oocyte maturation is a mature egg that has complete nuclear, plasma membrane and cytoplasmic changes that enable normal fertilization and subsequent development to occur. In vitro maturation has been achieved with viability of resulting eggs demonstrated by their fertilization and successful gestational development. Higher proportions of in vitro matured eggs develop from hormonally supported cultures of whole follicles than from cultures of extrafollicular oocytes. In vivo fertilization has been more useful in these efforts than in vitro fertilization. Accomplishments toward understanding the physiological mechanisms involved in oocyte maturation are encouraging and with improvements anticipated for in vitro fertilization technology it should become possible to efficiently combine these procedures at some future date. Such an advancement would open many doors beyond the new technologies in animal breeding of today. Exploitation of in vitro oocyte maturation might remove the present technical limitations imposed on dissemination of genetic offerings of desirable females.