This document presents the World Health Organization (WHO) operational framework for building climate resilient health systems. The framework responds to the demand from Member States and partners for guidance on how the health sector and its operational basis and health systems can systematically and effectively address the challenges increasingly presented by climate variability and change. This framework has been designed in light of the increasing evidence of climate change and its associated health risks; global, regional and national policy mandates to protect population health; and a rapidly emerging body of practical experience in building health resilience to climate change. Primarily intended for public health professionals and health managers, this framework would also help guide decision-makers in other health-determining sectors, such as nutrition, water and sanitation, and emergency management. International development agencies could use this framework to focus investments and country support for public health, health system strengthening and climate change adaptation. The objective of this framework is to provide guidance for health systems and public health programming to increase their capacity for protecting health in an unstable and changing climate. By implementing the 10 key components laid out in this framework, health organizations, authorities and programs will be better able to anticipate, prevent, prepare for and manage climate-related health risks. Least developed countries and countries in the process of developing the health components of National Adaptation Plans (NAPs) under the UN Framework Convention on Climate Change (UNFCCC) (4) may find this document particularly useful in their efforts to design a comprehensive response to the risks presented by short-term climate variability and long-term climate change.