This flagship report, with insights from across the network of the International Federation of Red Cross and Red Crescent Societies (IFRC), brings together the latest science, risk perception research and voices from affected communities. Produced by the IFRC and the Red Cross Red Crescent Climate Centre, the report provides a bottom-up perspective on extreme heat. Heat disrupts health, weakens social systems and triggers cascading failures in water, food and electrical and transport infrastructure. This report highlights the experiences of those who are most exposed, least heard and hardest hit. It will serve as a foundation for informed dialogue, strengthened partnerships and decisive steps towards protecting communities from one of the most urgent threats of the climate crisis.