A majority of women in their reproductive years experience a variety of symptoms premenstrually that can alter behavior and well-being and affect family, friends, and working relationships. Notwithstanding its prevalence, however, research has not yet clarified this inscrutable condition, commonly known as premenstrual syndrome (PMS) or more severe PMS, premenstrual dysphoric disorder (PMDD). This comprehensive review discusses the diagnosis, epidemiology, symptoms, etiology, and the complex web of biopsychosocial factors that attends PMS.