Chapter 27 of the 4th U.S. National Climate Assessment, Volume 2, assesses climate impacts, future risks, and adaptation in Hawai‘i and the U.S.-Affiliated Pacific Islands. The author team collaboratively developed the chapter’s Key Messages and narrative. Webinars and an informal survey of stakeholders informed the selection of focal sectors. To be inclusive of the vast region and expertise, the authors convened six half-day workshops on key sectors, including remote participation from experts in the U.S. Affiliated Pacific Islands. In all, the chapter involved more than 60 technical contributors. Authors reviewed major areas of risk and new understanding since the last national assessment, including on issues such as: (1) reliable and safe water supplies, (2) marine and terrestrial ecosystem health, (3) sea level rise and coastal impacts, (4) impacts on community livelihoods and well-being, including Indigenous peoples. Under these climate-related challenges to island sustainability, diverse groups are coming together to combine forward-looking policies with adaptation strategies. An integrated theme throughout the chapter is that early intervention can lower the economic, environmental, and social and cultural costs from a changing climate.