Abstract The clinical diversity of CMD is suggested by the different degrees of motor develop- mental delay, physical disability and muscle pathology, and by the variable presence of mental retardation. Most of the efforts aimed at delineating and subdividing the various CMD forms have originated from the International Consortium on CMD, that, under he auspices of the European Neuromuscular Centre (ENMC), has convened six dedicated workshops, whose proceedings have been published in Neuromuscular Disorders (Dubowitz 1994; 1997; 1999; Dubowitz and Fardeau 1995; Muntoni and Guicheney 2001). The classification proposed in this chapter, that takes into account the recent advances in the molecular genetic studies, is largely a reflection of the data presented at these workshops.