The thesis is written as four chapters detailing five studies through which the impact of overseas expeditions was investigated. Study 1 (Chapter 2) examined the effects of expeditions on the multidimensional self-esteem domains of youth participants. Results demonstrated significant and positive differences in post-test self-esteem domain scores for expedition participants compared with a control group. One of the multi-source data collections (i.e., the leader team) corroborated the significant effect for general self-esteem at post-test. However, only one significant maintenance effect was found for the self-esteem domain of honesty/trustworthiness at six months follow-up. In Study 2 (Chapter 3) an existing differentiated measure of transformational leadership was amended to provide a contextually relevant measure for use in the expedition setting, that is, the Expedition-DTLI (E-DTLI). The study was divided into three phases. Phase 1 explored the factorial validity of the new measure; following confirmatory factor analysis procedures and item deletion an acceptable model fit was provided, supporting a 7-factor structure. Phase 2 confirmed the factor structure, and phase 3 explored and confirmed the predictive validity of the E-DTLI. Taken together these results provide initial evidence that the E-DTLI is a valid measure for use in the expedition context. Using the E-DTLI, Study 3 (Chapter 4) examined the impact of transformational leadership (TL) on the multidimensional self-esteem domains of youth expedition participants. Regression analyses revealed that the hypothesised TL behaviours (intellectual stimulation, individual consideration) were significant predictors of certain self-esteem domains (e.g., general self-esteem, honesty/trustworthiness). Other predictive relationships that were not hypothesised were also evident (e.g., high performance expectations predicting general self-esteem). These results were used to inform Study 4 (Chapter 5) where a pilot TL training intervention was implemented. Results from the pilot indicated no significant difference in the experimental (intervention) group’s TL behaviours at post-test in comparison to the control group’s TL behaviours. However, the experimental group’s TL behaviours significantly increased pre to post test. Subsequent review of Study 4 led to amendments in content and design of the intervention, resulting in the development of a full-scale intervention (Study 5). Results for Study 5 (Chapter 5) demonstrated that the TL intervention had a significant and positive impact on experimental expedition leaders’ TL behaviours compared to the control group. When examining the self-esteem domains of the youth participants being led by the leaders, only the honesty/trustworthiness domain was significantly higher for the experimental leader group in comparison to the control group.