Extreme heat is Australia’s deadliest natural hazard — yet it often goes unseen. This report examines heat risk through the intersection of hazard, exposure, vulnerability and capacity, showing how impacts emerge across health, infrastructure, livelihoods and essential services. It clarifies key concepts — including extreme heat, heatwaves and urban heat islands — and explains Australia’s approach to measuring heat, defining thresholds and coordinating national alerts. The report identifies practical entry points for action across policy and community levels, providing a foundation for reducing urban heat risk.This report forms part of the first Post-Event Review Capability (PERC) on extreme heat, with the findings unfolding across three interconnected reports: Heat Stress at Work and Strengthening Resilience to Extreme Heat: An Adelaide Case Study. Together, they build a layered picture of how extreme heat risk is shaped, experienced and addressed.