Anti-Müllerian hormone (AMH), also called MUllerian inhibiting substance (MIS) is a product of supporting gonadal Sertoli and granulosa cells. Its main physiological role is the induction of regression of Müllerian ducts in male fetuses but it also plays a role in Leydig cell steroidogenesis and in follicular development. It is a member of the transforming growth factor B family and signals through two serine/threonine kinase receptors, only one of whom, type II, is specific. Type I receptors and the intracytoplasmic signaling molecules are shared with the bone morphogenetic family. AMH is positively regulated by SF1, SOX9 and FSH. Testosterone is a powerful downregulator. Males lacking functional AMH or AMH receptor genes do not undergo regression of MUllerian derivatives during fetal life. AMH is an excellent marker of prepubertal testicular function and has gained recognition as a valuable marker of follicular reserve in adult women.