The Climate Action Team’s Public Health Workgroup convened a subcommittee, the Heat Adaptation Workgroup, to develop this document. The Heat Adaption Workgroup was co-chaired by the California Department of Public Health (CDPH) and the California Environmental Protection Agency (Cal/EPA) and includes staff from multiple State agencies. (See the Acknowledgements for the full list of participating agencies and departments, page 21). As the climate changes in California, extreme heat is projected to be a growing problem that will have health, economic, ecological, and social impacts. Actions taken by government agencies and other entities in the coming years could mitigate the effects of extreme heat and reduce resulting disabilities and deaths. This document provides guidance for incorporating extreme heat projections, based on current climate change models, into planning and decision making in California. This guidance provides an overview of current climate projections for increased temperature and extreme heat conditions for California, describes the health effects of extreme heat, and presents recommendations for state and local planners, local governments, emergency response, and public health and health care professionals and institutions. The early integration of extreme heat projections into plans, policies and projects will lessen the potential impacts of the state’s warming climate, as will modifications made to cool the built environment of urbanized areas where over 95% of California’s population lives. The guidance does not attempt to look at the many indirect effects of increased temperature, such as wildfire, drought, and changes in agricultural production, that are expected to pose additional challenges to human health and well-being in California. Although increased temperatures related to climate change will affect the built environment and service delivery systems, these issues are not directly addressed here. Several state resources provide a more comprehensive overview of climate change impacts and adaptation information and planning guidance, including the impacts of heat beyond the health effects addressed in this Guidance.