Excessive heat events (EHEs) are and will continue to be a fact of life in the United States. These events are a public health threat because they often increase the number of daily deaths (mortality) and other nonfatal adverse health outcomes (morbidity) in affected populations. Distinct groups within the population, generally those who are older, very young, or poor, or have physical challenges or mental impairments, are at elevated risk for experiencing EHE-attributable health problems. However, because EHEs can be accurately forecasted and a number of low cost but effective responses are well understood, future health impacts of EHEs could be reduced. This guidebook provides critical information that local public health officials and others need to begin assessing their EHE vulnerability and developing and implementing EHE notification and response programs.