State and local governments, businesses, community organizations, and the general public are taking an increasingly significant role in climate impact assessment. Driven by impacts to constituents and customers and threats to human health, essential services, and property values, local organizations are on the front lines of responding to climate change. National and international efforts such as the U.S. National Climate Assessment and Intergovernmental Panel on Climate Change provide fundamental scientific understanding as well as methods and modeling tools. Subnational climate assessments can build on this foundation and tailor models and analyses to specific local or decision contexts. However, subnational climate assessment and adaptation presents new scientific and research challenges, such as those related to downscaling climate models, simulating extreme events, and understanding local values and institutional practices. As state, local, and sectoral assessments become more common across the nation, there is a critical opportunity to share learnings and identify challenges and pitfalls. Building off a National Academies of Sciences, Engineering, and Medicine activity focusing exclusively on subnational climate assessment, we consider the methods and results from a variety of examples to synthesize findings about current practices and the future of subnational climate assessment. Plain Language Summary: Climate assessments provide descriptions of the current and future impacts of climate change. Such assessments have long been a part of national and international activities on climate change. Increasingly, state and local governments, businesses, and other groups have begun climate assessments that address possible impacts from climate change specific to their constituents or customers. When taking national and international efforts to a local level, two important challenges arise. One is related to the challenge of applying science and modeling developed for the large scale to a smaller scale. The second is the need to translate technical analysis into usable information for decision makers and the public. Here we build off of a workshop convened by the National Academies of Sciences, Engineering, and Medicine to consider these issues. Key Points: State and local governments and others are taking an increasingly significant role in climate impact assessmentSuch assessments present analytical challenges from downscaling national models, simulating extremes, and integrating local perspectivesThe evolution of California's assessments, in its fourth iteration, reflects the demands for climate assessments to translate science into response activities [ABSTRACT FROM AUTHOR]