Relational developmental systems metatheory frames many contemporary models of human development, including two strengths-based approaches to enhancing the lives of diverse children and adolescents, the positive youth development (PYD) perspective and resilience science. Both approaches emphasize the potential for plasticity in human development, and the systematic changes that arise through mutually influential relations between the individual and the multiple, integrated levels of the dynamic developmental system. After discussing the similarities and differences in these two approaches, different models of PYD are discussed in relation to how descriptions, explanations, and attempts at optimizations of the development of diverse youth are enacted within these conceptions. The substantive and research challenges associated using PYD models to enhance the lives of diverse global youth are highlighted, and the implications for future PYD research in international settings, and specifically among poor youth developing within the majority world, are discussed.