Publisher Summary This chapter discusses control of ovulation by the anterior pituitary gland. Arguments are brought forward in the chapter pointing to the participation of structures situated outside the preoptic area and the hypothalamus in spontaneous ovulation. With respect to the ovulatory action of estrogen, arguments that point to a site of action situated in the mediobasal hypothalamus and pituitary gland—although there are some indications that other structures within the central nervous system (CNS) are also involved—are discussed. With respect to the action of progesterone, a hypothesis that might explain its action within the hypothalamus is explored. Finally, the results presented indicate that the effects of cuts in the CNS may vary according to the time elapsed between making these lesions and the experiment. The possibility that after deafferentation a certain degree of reorganization can occur has to be considered.