Effective prevention in a city requires a portfolio of actions at different levels: from health system preparedness coordinated with meteorological early warning systems to timely public and medical advice and improvements to housing and urban planning. These actions can be integrated in a defined Heat Health Action Plan. There are several principles that should be used in planning for and responding to heatwaves. This Masterclass is an introduction to heat health action planning, based on principles and guidance developed by the World Health Organization and from case studies of actual plans.