The hormonal correlates of reproductive aging and the menopause transition reflect an initial loss of the follicle cohort, while a responsive ovary remains, and an eventual complete loss of follicle response, with persistent hypergonadotropic amenorrhea. The physiology of the process is described, along with key findings of relevant studies, with an emphasis on the Study of Women's Health Across the Nation. A clinical framework is provided to help clinicians to forecast the major milestones of the menopausal transition and to predict potential symptoms or disease.