Of 1.2 billion adolescents in the world today, 90% live in low- and middle-income countries. These adolescents not only face many challenges but also represent a resource to be cultivated through educational opportunities and vocational training to move them toward economic independence, through initiatives to improve reproductive health, and through positive interpersonal relationships to help them avoid risky behaviors and make positive decisions about their futures. This volume tackles the challenges and promise of adolescence by presenting cutting-edge research on adolescent social, emotional, behavioral, cognitive, and physical development; promising programs from different countries to promote adolescents’ positive development; and policies that can advance adolescents’ rights within the framework of international initiatives, such as the Convention on the Rights of the Child and Sustainable Development Goals, which are guiding the international development agenda through 2030. This volume seeks to provide actionable strategies for policymakers and practitioners working with adolescents. Disconnects between national-level policies and local services, as well as lack of continuity with early childhood responses, present a significant challenge to ensuring a coherent approach for adolescents. Increasingly, adolescent participation and demands for rights-based approaches are seen and often unfortunately conflated with violence. This volume adopts a positive framing of adolescence, representing young people as opportunities rather than threats, and a valued investment both at individual and societal levels, contributing to a positive shift in discourses around young people.