Ovarian function in adults is controlled by hormones circulating in the body. The primary hormone responsible for cyclicity in animals and humans is estrogen. Estrogen is mostly produced in the ovary and enters the circulation where it then signals the brain for a response. The parts of the brain that controls reproductive hormones are the hypothalamus and anterior pituitary. Estrogen stimulates the hypothalamus to produce gonadotropin releasing hormone, which in turn signals the anterior pituitary to produce follicle stimulating hormone and luteinizing hormone. These hormones enter the circulation and signal the ovary to ovulate. Substances with estrogenic activity can potentially interfere with this signaling if levels of activity are sufficient to cause a response. Soy foods contain estrogenic substances called phytoestrogens. The predominant phytoestrogens found in soy are genistein and daidzein. The female reproductive system is dependent on hormones for proper function and phytoestrogens at very high levels can interfere with this process. This paper summarizes the literature on adult soy consumption and its effect on ovarian function.