Te menstrual cycle is the result of an orchestra of hormones. It involves the interaction of many endocrine glands as well as a responsive uterus. Te menstrual cycle remains a complex process where many aspects are still not well understood. In this chapter we will examine the control of the menstrual cycle through the interaction of the central nervous system, namely, the hypothalamus and pituitary, and the ovaries, resulting in the cyclic and ordered sloughing of the uterine endometrial lining. Te frst section of this chapter, Te Menstrual Cycle, will review the phases of the menstrual cycle. In the second section, Anatomy of the Menstrual Cycle, the hypothalamic, pituitary, ovarian, and uterine activities will be reviewed. Te key hormones that play a role in the control of the menstrual cycle include gonadotropin-releasing hormone (GnRH), follicle- stimulating hormone (FSH), luteinizing hormone (LH), estradiol, and progesterone (. Table 1.1). In addition to these key hormones, there are other peptide and non-peptide hormones that play a role in the menstrual cycle that will also be discussed. Tese hormones will be discussed in the third section, Endocrinology of the Menstrual Cycle.