This thesis explored and evaluated the appropriateness of established psychological theories for understanding mental toughness development in adolescents. Initially, adolescent performers’ perspectives about mental toughness development were grounding in Bronfenbrenner’s (2001) bioecological model. Subsequently, self-determination theory (SDT, Deci & Ryan, 1985b, 2000) was considered. This theory was selected because of its consistencies with the bioecological model and initial findings, as well as its potential to inform applied protocols. Significant theoretically-expected associations were identified between SDT principles and mental toughness, as well as mental toughness and other meaningful outcomes. The effectiveness of an intervention informed by SDT principles was then evaluated. Although findings did not support the hypotheses, several barriers and obstacles to adopting SDT principles in practice were identified. To elucidate the hypothesised associations, a conceptual essay that detailed the value of SDT for understanding mental toughness was presented. This essay conceptualised mental toughness as comprising notions of striving, surviving, and thriving. It is hoped that researchers will continue to investigate the development of mental toughness along the lines pursued in this thesis and, at the same time, attend to recommendations proposed throughout.