To this juncture, clinical management, teaching of medical providers, and the design and interpretation of clinical trials has been hampered by the absence of a consensus system for the classification of causes or potential causes of abnormal uterine bleeding (AUB). Indeed, more than one possible mechanism may be involved in the development of the bleeding symptoms experienced by a given individual. A consistent and universally accepted classification system could be used by clinicians, investigators, and even patients to facilitate communication, clinical care, and research. The "PALM-COEIN" AUB classification system is the result of several years of collaboration among a spectrum of individuals involved in clinical medicine, teaching, and the basic and clinical sciences and is proposed as a tool that meets the requirements just described but one that is capable of adaptation to our evolving insight into the mechanisms involved in the genesis of AUB. This system has been accepted by the International Federation of Gynecology and Obstetrics (FIGO) as a suitable system for widespread international use.