While Comprehensive Community Initiatives (CCIs) provide promising avenues to support the positive development of all young people, research findings assessing the relation between CCIs and community-level child and youth outcomes have been mixed. Although there are exceptions, few evaluations on the impact of CCIs on positive youth development have been conducted. In this edited collection, the authors draw on the field of developmental science to provide a basis for why CCIs are a powerful tool for providing all young people with opportunities to thrive. The collection begins with a brief history of CCIs and their impacts to illustrate why a developmental framework is needed, followed by a discussion of the editors' proposed framework. Each chapter that follows offers some of the most rigorous research and extant knowledge of CCIs. In the final chapter, the editors provide recommendations for future research that can systematically explore the impact of CCIs, better indicating their effectiveness and offering proven strategies that can be implemented in varying contexts. Altogether, this collection offers researchers and practitioners in the field a means by which to better incorporate theory into the vision and practices of CCIs and, as such, the tools to better measure the outcomes of the CCIs.