I. Introduction II. Defining the Perimenopause III. Classic Studies of the Perimenopause A. Historical studies B. Early reports of women’s experiences in the perimenopause C. Early prospective menstrual cycle interval and basal temperature documentation IV. Prospective Epidemiological Studies of the Perimenopause A. Manitoba Project on Women and Their Health in the Middle Years B. Massachusetts Women’s Health Study C. Kuopio Osteoporosis Risk Factor and Prevention (OSTPRE) Study V. Systematic Studies of the Endocrinology of the Perimenopause A. Cross-sectional (single-cycle) hormonal studies in the perimenopause B. Prospective ovarian hormonal levels in the perimenopause VI. Histological Studies of Ovarian Changes Across the Lifespan VII. Physiological Studies of Changing Ovarian Hormones in Women in Their Forties and Fifties A. Folliculogenesis and ovarian hyperstimulation for in vitro fertilization (IVF) B. Inhibin physiology in women over forty VIII. Hypotheses to Explain Perimenopausal Endocrinology A...