This thesis provided an in-depth examination of mental toughness in sports performers, and comprised three studies, of which Study 3 contained two parts. The aim of the thesis was to: define mental toughness, identify its component parts, devise a working framework of mental toughness, and identify the underlying mechanisms involved in the development and maintenance of mental toughness. Study 1 addressed the definition of mental toughness and its essential components using 10 international performers. The proposed definition emphasized both general and specific dimensions , and 12 attributes fundamental to the ideal mentally tough performer. These covered self-belief, desire/motivation, dealing with pressure and anxiety, focus (þerformance and lifestyle related), and pain/hardship factors. Study 2 built upon the findings of Study 1 in a sample of eight Olympic or World Champions, three coaches, and four sport psychologists. Findings verified the definition, and identified 30 attributes that were developed into a working framework of mental toughness. The 30 attributes were found to cluster into 13 subcomponents and four dimensions within an overall working framework: a general dimension (attitude/mindset), and three time-specific dimensions (training, competition, post-competition). Study 3 re-interviewed l1 of the participants from Study 2 regarding: (a) the development and maintenance of mental toughness, and (b) how the framework dimensions and subcomponents interacted during the development and maintenance process. Findings revealed four distinct career phases in the development and maintenance of mental toughness. Critical incidents, both positive and negative, were perceived to act as catalysts in cultivating mental toughness, and once acquired, mental toughness needed to be maintained. Findings also confirmed the development and subsequent maintenance of mental toughness over three stages. Factors affecting development and maintenance included: stage l, skill mastery and socialization; stage2, competitiveness, successes in training and competitions; and stage 3, international competitive experience, education, the use of mental skills, a wide ranging social support network, and reflective practice. This prolonged research program has resulted in an empirically based definition of mental toughness, the development of a framework depicting its component parts, and provided an in-depth understanding of the mechanisms involved in the development and maintenance of mental toughness. Practical implications indicate that mental toughness develops over three distinct stages, in the dimensional order of attitude/mindset, training, competition, and post-competition, and requires maintenance. Future directions are discussed in relation to measurement and intervention strategies.