Positive youth development is a holistic approach that considers both internal (e.g., life skills and positive psychosocial characteristics) and external (e.g., coach and parent) developmental assets. The positive youth development framework has largely been used to examine multi-sport and recreational/high-school level programmes as a means to understand how participation within these environments can contribute to positive psychosocial development. The aim of the present thesis, comprised of four distinct studies, was to understand how a positive youth development approach might be applied to and integrated within the performance environment of British swimming. Study 1 comprised a two-stage investigation focused on identification and consensus related to a specific set of psychosocial assets appropriate for swimming. Following a content analysis of existing literature, a dialectical methodology was utilised to interview a panel of 10 experts from professional (coach and practitioner) and academic fields within swimming and youth sport. Five higher order categories containing 17 internal assets emerged; namely, self-perceptions, behavioural skills, social skills, approach characteristics and emotional competence. In Study 2, coaches (n=181) attitudes towards and perceptions of the 17 psychosocial assets were examined via a bespoke quantitative survey. The five-factor higher order model that emerged from the first study was quantitatively tested and supported. Coach characteristics were also examined regarding coaches overall value of the assets. Results indicated that assets within self-perceptions, behavioural skills and approach characteristic groups were more valued than those within social and emotional categories. Full-time, paid coaches provided higher value ratings for all asset groups compared to part-time, volunteer coaches. Study 3 replicated and extended Study 2 by examining attitudes of British swimming parents (n=249) towards the psychosocial assets, in conjunction with perceptions of their parenting style and levels of social support provided to their children within a swimming environment. Structural equation modelling was used to test hypothesised relationships between parental perceptions of parenting style, social support availability and value placed on the five internal groups of assets. Results indicated that parents asset value profiles were very similar to those of swimming coaches, with swimming specific assets of self-perceptions, behavioural skills and approach characteristics valued more than the less specific assets within social and emotional subgroups. Further, parents who reported high levels of esteem support also placed greater value on all assets apart from self-perceptions, and parents who reported a warm style were more likely to provide this esteem support. vi Finally, Study 4 examined perceptions of autonomy supportive coach and parenting styles and social support availability in addition to motivational goal orientation, perceived sport competence and self-esteem in a sample of 246 swimmers. Hypothesised relationships between coach and parenting style, perceived social support availability and the asset related outcomes were tested using structural equation modelling. Results revealed that autonomy supportive coach and parenting styles both positively predict respective perceptions of social support availability. Athletes also reported that coach social support positively predicted both task and ego orientation, while parental emotional support positively predicted task orientation only. Both task and ego orientation positively predicted perceived sport competence which, in turn, positively predicted self-esteem. Overall, the findings of this thesis revealed a comprehensive list of internal assets that were highly valued by both coaches and parents, although the assets contained within the social and emotional groups were valued to a lesser degree, prompting calls for greater awareness on the relevance and applicability of these assets within British swimming. Furthermore, the styles that coaches and parents operate within positively predict the types of perceived social support availability which, in turn, predict internal asset value and level. Specifically, an autonomy supportive coaching style and a parenting style characterised by a high degree of warmth are both thought important elements to promote, with parental esteem and emotional support found to be most related to internal asset value and level, respectively. Links between social support, motivational goal orientation, perceived sport competence and self-esteem were also tested and supported. Overall, therefore, this thesis provides a unique contribution to the sport psychology and positive youth development literature by illustrating key areas of development (i.e., the internal assets) and by demonstrating one mechanism through which a degree of this development occurs (i.e., social support).