Climate assessment activities are increasingly driven by subnational organizations--city, county, and state governments; utilities and private companies; and stakeholder groups and engaged publics--trying to better serve their constituents, customers, and members by understanding and preparing for how climate change will impact them locally. Whether the threats are drought and wildfires, storm surge and sea level rise, or heat waves and urban heat islands, the warming climate is affecting people and communities across the country. To explore the growing role of subnational climate assessments and action, the National Academies of Sciences, Engineering, and Medicine hosted the 2-day workshop on August 14-15, 2018. This publication summarizes the presentations and discussions from the workshop.