Myasthenia gravis (MG) is an autoimmune disorder, in which end-plate membrane damage is induced by antibodies directed toward various epitopes of the main immunogenic region of the nicotinic acetylcholine receptor (AChR). This article reviews the mechanisms responsible for the development of MG. Recent investigations into the roles of the thymus, antibodies against AChR, cytokines, and neuromuscular transmission have given new insight into the pathogenesis of MG. These new advances have led to a better understanding of the immune mechanisms in MG and have opened new therapeutic horizons.