Skeletal muscle satellite cells, which reside beneath the basal lamina of mature muscle fibers, function as myogenic precursors and are required for normal muscle growth and repair. Satellite cells share a common anatomical localization, yet they exhibit substantial phenotypic and functional heterogeneity. Recent efforts in the field of adult myogenesis have been aimed at dissecting this heterogeneity and reveal the presence of discrete cell lineages within the muscle that function independently and interactively to maintain muscle homeostasis and to determine the outcome of muscle damage. Normal developmental regulation of the frequency and function of these distinct tissue precursors, and pathological deregulation of their activity, may have an important role in age- and disease-dependent loss of muscle regenerative activity.