Background: The International Federation of Gynecology and Obstetrics (FIGO) systems for nomenclature of symptoms of normal and abnormal uterine bleeding (AUB) in the reproductive years (FIGO AUB System 1) and for classification of causes of AUB (FIGO AUB System 2; PALM-COEIN) were first published together in 2011. The purpose was to harmonize the definitions of normal and abnormal bleeding symptoms and to classify and subclassify underlying potential causes of AUB in the reproductive years to facilitate research, education, and clinical care. The systems were designed to be flexible and to be periodically reviewed and modified as appropriate. Objectives: To review, clarify, and, where appropriate, revise the previously published systems. Methodology and outcome: To a large extent, the process has been an iterative one involving the FIGO Menstrual Disorders Committee, as well as a number of invited contributions from epidemiologists, gynecologists, and other experts in the field from around the world between 2012 and 2017. Face-to-face meetings have been held in Rome, Vancouver, and Singapore, and have been augmented by a number of teleconferences and other communications designed to evaluate various aspects of the systems. Where substantial change was considered, anonymous voting, in some instances using a modified RAND Delphi technique, was utilized.