This learning activity examines heat-related illness (HRI) across the lifespan, equipping registered nurses with the clinical knowledge needed to identify at-risk patients, recognize HRI along its full spectrum, and apply evidence-based prevention and intervention strategies. Topics include age-related thermoregulatory physiology, medication effects on heat tolerance, clinical differentiation of heat exhaustion from heat stroke, and cooling interventions. The content also addresses health equity considerations and the social determinants that amplify heat vulnerability in high-risk populations.