Mental toughness is accepted to be an important component of sporting performance, especially so in the domain of cricket. It has been called many names, such as Big Match Temperament, bottle, and mettle and it is widely believed that it plays a role in how successful a cricketer may be, although very difficult to define and explain. James Loehr described it as one’s ability to consistently perform to the upper limit of your talent and skill and numerous researchers have since tried to define the construct based on more empirical research. This research project consists of three articles on mental toughness. The first focuses on the consideration of extra-personal influences on the development and implementation of mental toughness programmes. The second focuses on examining the psychometric properties of the paper-and-pencil versions of the Sports Mental Toughness Questionnaire (SMTQ) and the Psychological Performance Inventory-Alternative (PPI-A). The third examines the differences in the demographic characteristics of a sample of cricketers on the online versions of the SMTQ and the PPI-A. The results suggest that extra-personal influences are exceptionally important in the development and implementation of mental toughness programmes for school level cricketers, especially motivational climate and social support. While the PPI-A and the SMTQ displayed some promising psychometric properties in the current study, researchers should apply these mental toughness inventories with circumspection, taking into account questions regarding dimensionality, item formulation and variation in sample characteristics (e.g., age and sporting code), until more research can be conducted using these inventories with larger and more varied samples and the understanding of the mental toughness construct improves. The examination of the demographic differences on scores of the SMTQ and PPI-A revealed inconclusive results on age, sex, and ethnicity, while competitive level was the only distinguishing characteristic in which respondents at high levels produced higher mental toughness scores. The three studies comprising this “by articles” format PHD dissertation will be referred to as Article 1, Article 2, and Article 3 and can be found in Chapters, 2, 3, and 4 respectively. / Psychology / D.Phil. (Psychology)