Prosociality describes the tendency to engage in behaviours that aim to enhance or maintain the well-being of others, for example, sharing and co-operating. In children and adolescents this trait is often viewed as a core aspect of social competence and an important developmental outcome. Prosociality may also play an important role in how young people navigate their increasingly complex social world. This raises the question of whether individual differences in prosociality are related to young peoples’ well-being, such as their risk of developing psychological problems. The goal of the current series of research was to explore this question. A series of four studies was designed to answer this question. This research made use of pre-existing survey data, including the “mental health of children and young people in Great Britain, 2004” survey (Papers 3 & 4) and the “Understanding Society” survey (Paper 2), enabling access to large sample sizes. In Paper 1, a meta-analysis was undertaken to determine the nature of the relationship between prosociality and two important clinical outcomes, internalizing disorder and low self-esteem. This review identified a significant but small relationship between greater prosociality and reduced internalizing disorder or low self-esteem. In Paper 2, a longitudinal study explored the relationship between prosociality and well-being over a 1-year-period in children and adolescents. This study did not identify any prospective effect of prosociality upon subsequent changes in well-being. Two further studies explored the factors that may influence whether prosociality is linked to well-being. In Paper 3 the possibility that existing measures of prosociality may partly account for the small or null relationships observed so far (Papers 1 & 2) was explored by developing and validating a new measure of prosociality. This new measure appeared psychometrically robust and demonstrated advantages over pre-existing scales of prosociality. In Paper 4, a cross-sectional study was undertaken to explore whether the discrepancy in young peoples’ self-ratings and parental ratings of prosociality has a relationship with emotional problems (i.e., depression and anxiety). A moderator analysis found that self-rated and parent-rated prosociality may interact to determine risk of psychological problems in young people. This study suggested that the discrepancy in ratings of prosociality may be more important in predicting psychological problems than overall ratings by individual informants. Results support the relevance of prosociality to well-being in young people and highlight how factors such as the measurement of prosociality and the interpersonal context within which it occurs impact upon this relationship.