Müller's superior tarsal muscle has been extensively studied by anatomists and physiologists but has been largely ignored by surgeons. This muscle is considered from the standpoint of both gross and finer anatomy. Concepts regarding the uncertain course of its sympathetic nerve supply fibers are reviewed, and "semi-conclusions" are given. The physiology of the muscle, both normal and pathological, is considered in view of both accepted and controversial concepts. Methods of weakening an overactive Müller's muscle medically and surgically are discussed. Some methods that have attempted to utilize the lid-elevating power of Müller's muscle are described, and the muscle's potential in this regard is considered. This small muscle is deserving of more appreciation and of a higher surgical status than it has received in the past.