The musculoskeletal system undergoes rapid and complex changes during adolescence, driven by mechanical, hormonal, and genetic factors. Among these changes, the development of muscle and the accrual of peak bone mass play a pivotal role in determining long-term physical health and performance capacity. This chapter comprehensively examines the development of muscles, tendons, bones, and joints during this critical life stage, emphasizing key mechanisms such as mechanotransduction, fiber type transitions, and bone remodeling. It explores the interplay of modifiable factors, including physical activity, nutrition, and environmental context, with nonmodifiable determinants such as sex, hormones, and genetics. Particular attention is given to the differential adaptation rates of muscle and tendon, sex-specific injury risks, and the impact of energy availability on tissue development. The chapter integrates recent findings on overuse, underload, and functional adaptations to guide evidence-based strategies aimed at promoting lifelong musculoskeletal health and performance.