Despite recent advances in molecular genetics, it has proven very difficult to arrive at an accurate and clinically useful classification of the muscular dystrophies. Much of this difficulty arises from confusion related to the term "muscular dystrophy" itself, as well as a general reluctance on the part of the neuromuscular community to abandon traditional, clinically based classifications. Nevertheless, advances in the understanding of the molecular defects of these disorders have permitted a foundation for classification based on molecular biology. This review presents a historical perspective on the classification of the muscular dystrophies, and furnishes the underpinnings of a genetic classification that can be used both at the bedside and in the research laboratory.