Project Summary Parks are a key feature of the built environment that foster community engagement, make communities vibrant, and support resident wellbeing. This study will test the impact on community-level health-related quality of life and mental health of a community-engaged, community-level intervention that aims to improve park-based health and social programming. The study will leverage neighborhood parks that have recently been redesigned and renovated as part of the Community Parks Initiative, a capital investment and park equity program in New York City. We aim to work with eight lower income and predominantly Latino and Black neighborhoods through an asset-based and human-centered design process to co-create and implement one health and one social strategy in each neighborhood park. The health strategy will focus on physical activity and the social strategy will seek to enhance social relationships and networks in each neighborhood. Achieving broad reach, inclusivity, and sustainability are key factors that will be taken into account in the design process. The eight neighborhoods will be cluster-randomized to one of two steps in a stepped wedge intervention trial. The intervention is 24 months in each community, with follow-up to 48 months. We will study outcomes, including HR-QoL, depression, anxiety, stress and loneliness, at the community level (not among individuals participating in park activities) via random, representative samples of adult residents in participating communities at intervention baseline and months 24 and 48 post-baseline.In addition, we will examine whether the intervention effects might be mediated through social cohesion, neighborhood ties, sense of community, park use and perception and/or health behaviors such as physical activity and sleep. Finally, we will conduct qualitative research to examine the implementation of the community-level intervention based on constructs from the Consolidated Framework for Implementation Research. Study findings will help inform future best practices in urban community development and park programs and policies to promote population health and reduce health disparities.