Discovery of the gene encoding the protein dystrophin delineated not only the cause of Duchenne dystrophy but also an expanding family of at least eight different dystrophin-associated muscle proteins. These include two that span the membrane (the dystroglycans), at least five within the membrane (the sarcoglycans), and a submembrane protein (utrophin). In recent years, defects in the genes for several of these proteins have been identified in several different muscular dystrophies. The spectrum of clinical deficits associated with these genetic lesions is broad, but typically it encompasses both milder proximal myopathies characteristic of limb-girdle dystrophy and more severe disorders reminiscent of Duchenne dystrophy. These discoveries will provide the basis both for improved understanding of physiology of this complex of proteins at the muscle membrane and for new strategies in the treatment of muscular dystrophy.