Grounded in the Positive Youth Development (PYD) approach and in Bronfenbrenner’s ecological model of human development (1979), the current research program used a correlational approach to examine the effect of participation in organized activities (OAs) on two dimensions of youth’s psychological and emotional development: Psychological adjustment (Article 1) and Emotional competence (Article 2). Through two articles and four studies, this research program also aimed to explore the influence of two OA-context variables, youth experiences and youth engagement, on the previous dimensions of development. Together, results aimed to provide new information in the PYD research domain. Main findings are described. First, we hypothesized that participation in OAs had a positive effect on indicators of youth psychological and emotional development. Overall, our results indicated that this effect was not statistically significant (Article 1, Study 2; Article 2, Studies 1 and 2), although some statistically significant differences were found between OA participants’ and non-participants’ psychological adjustment in a correlational design (Article 1, Study 1). The potential implications of these results, as well as their limitations, are discussed. The current research also examined the potential role of youth experiences within their OAs in the link between OA participation and psychological and emotional development. Overall, results indicated that some experiences in OA contexts were statistically significant predictors of psychological adjustment and emotional competence. Furthermore, experiences of identity emerged as mediators of the effect of participation on life satisfaction in a longitudinal design (Article 1, Study 2). However, this effect was negative and may be best explained by the presence of a suppression effect in the model. Moreover, experiences of initiative and stress emerged as mediators of the effect of participation on emotional competence (Article 2, Study 1), but results were not replicated in a longitudinal design (Article 2, Study 2). This research also examined the potential role of youth’s engagement in their OAs on psychological and emotional development (Article 1, Study 2; Article 2, Study 2). The inclusion of engagement in our research program was crucial and allowed for the identification of specific necessary conditions for participation to have an effect on outcomes of psychological and emotional development. In our research, engagement emerged as a moderator of the indirect effects of participation on two indicators of psychological and emotional development. First, the indirect effect of participation on self-esteem through experiences of initiative emerged as statistically significant only for youth who were highly engaged in their OA (Article 1, Study 2). Next, the negative indirect effect of participation on life satisfaction through experiences of identity emerged as significant only for youth who were highly engaged in their OA. Again, the latter result might be best explained by the presence of a suppression effect (Article 1, Study 2). Lastly, engagement also emerged as a moderator of the effect of participation on specific youth experiences (Article 1, Study 2). Implications for theory and practice emerge from this research. A better understanding of the effect of OA participation on psychological and emotional development and of the specific roles of youth experiences and youth engagement in OAs is attained. Practical implications are discussed. In line with its exploratory nature, the current research program provides multiple avenues for future research within the PYD approach.