Humans differ from most other animals by having a fairly long lifespan and, proportionately, a long period of growth before adult morphology is attained. This chapter considers body composition changes associated with childhood, adolescence and adulthood from a health perspective, before considering in more detail how body composition can be adjusted in the context of sport. Although this might sound straightforward, consider that it might take 12 years of sports participation before a world class athlete attains a career best. Future capability needs to be recognised, understood and nurtured during childhood, while maintaining present health and safeguarding future health. Excessive training perturbs the body's homeostasis in musculo-skeletal, metabolic, endocrine, immune and psychological domains; however, it appears that individual tolerance of high exercise volume and susceptibility to overtraining is highly variable. Variability in the tempo of maturation in children can represent an advantage or disadvantage depending on the sport and gender. Knowledge of these issues is important for exercise practitioners and coaches alike, given the growing number of people whose body composition either predisposes them to increased risk of disease, or requires their body composition to be optimised in order to enhance performance and reduce injury risk. In this chapter we consider how kinanthropometry can be useful in youth sports for talent development and improving sports performance. We will explore the relationship between structure (as measured by anthropometry), physiology, psychology and skill for talent identification and how using these factors in isolation may risk overlooking potential champion athletes. We outline how to predict adult size and proportions from the growing child (morphological prediction), the optimal size and proportions for the ideal sports performance (morphological optimisation) in sport, and how athletes can tailor soft tissue for maximum functional effectiveness by training, tapering, etc. (morphological prototype). In addition, we examine how performance might be enhanced or retarded by biological maturity and how biological maturity is affected by energy balance in the young athlete.