The seemingly never-ending search for vitality and youthfulness in men has been and continues to be at the forefront of the ideal male image, which is further popularized by our society. As such, it comes without surprise that the anabolic effect of testosterone remains a riveting area for further exploration, both for research purposes among the scientific community and for image-enhancing purposes among the lay public. The biological plausibility of testosterone’s role in muscle anabolism stems from studies demonstrating that androgens promote the commitment of pluripotent mesenchymal stem cells into myogenic lineage while inhibiting their differentiation into adipocytes. Epidemiological studies have shown an association between endogenous serum testosterone concentrations with body composition, muscle strength, and both self-reported and performance-based measures of physical function. Anabolic effects of exogenous testosterone administration in various patient populations have also been studied for decades and have consistently shown that administration of testosterone increases muscle mass and strength, while positive effects on physical function in older men have been less consistent. In this chapter, we provide an overview of the mechanisms by which androgens promote anabolism followed by studies of testosterone (and other androgens) therapy in both healthy men and men with chronic medical conditions.