This article reviews recent evidence concerning the development of mental toughness in young athletes, from first involvement in sport through to early adulthood. The role and importance of genetics, environmental factors, and psychological-skills training in the development of mental toughness is discussed. In particular, environmental factors that can be manipulated and influenced by coaches and parents are emphasized to aid the transfer of knowledge from scientific research into applied practice. Of central importance is the development of independent problem-solving and personal responsibility through a challenging yet supportive learning environment. We argue that to develop mental toughness, young athletes must be gradually exposed to, rather than shielded from, demanding situations in training and competition in order to learn how to cope. Also, as athletes become more emotionally mature, they should become increasingly involved in making decisions regarding their own development. Athletes should be encouraged and supported in reflecting upon setbacks and failures that occur as a natural part of the developmental process. Negative experiences, as well as the confidence-boosting outcomes of achieving goals, provide opportunities for personal growth, and allow important lessons to be learned. Various practical suggestions are provided.