Complete Streets is an urban planning paradigm that seeks to utilize streetscapes as holistic space and not merely as a means for conveyance. This paradigm seeks to provide equitable access for all street users across all modes of transportation, improving urban livability and reducing reliance on car ownership. In the first chapter of this dissertation, we compare the primary benefits of Complete Streets valued by practitioners with the secondary benefits promised by academics and Complete Streets advocates, and suggest a methodology for empirically quantifying spatiotemporal outcomes of infrastructure projects. In the second chapter, we review literature related to Complete Streets outcomes to determine which benefits are well-documented and which rely on logic pathways. We then survey Complete Streets practitioners across the US to find trends in current practice and identify heterogeneities. In the third and final chapter, we develop a Capability Maturity Model for Complete Streets programs. This model identifies seven dimensions of agency practice that are fundamental to robust implementation of Complete Streets policies and guides practitioners through a self-evaluation. The purpose of the model is to allow agencies to evaluate their current agency capability and evolve to a more mature form of practice. Expected outcomes of this model include improved inter-agency communication and collaboration, identification of useful technologies and best practices, and a culture that values equitable transportation decisions and endures through changes in administration..