This working paper builds the policy case for why sustainability presents small-to-midsize legacy cities with a promising pathway for their regeneration. Its conceptual foundation rests at the intersection of three critical lines of analysis: existing sustainability efforts in cities, the unique challenges and opportunities of small and midsized legacy cities, and the challenges and constraints of operating and innovating in smaller cities. While researchers have examined sustainability within legacy cities, most attention has been paid to the policies, plans, and programs from large legacy cities, such as Detroit, Baltimore, Cleveland and Philadelphia. We found little research or policy analysis about the opportunities, challenges, and promising practices for sustainability within small-to-midsize legacy cities. Building on our scan of current sustainability initiatives in smaller and midsize legacy cities (Greenventory 1.0), this working paper seeks to shine a light on the opportunities, success, and challenges faced by this cohort of small-to-midsized legacy cities that are often overlooked at the intersection of legacy cities and sustainability. Our theory of change argues that green and sustainable policies, plans, programs, projects and practices can catalyze, facilitate and sustain the revitalization and regeneration of small-to-midsized legacy cities.