The World Health Organization (WHO) is a specialized institution of the United Nations (UN), established to coordinate international public health efforts and promote the attainment of "the highest possible level of health" for all peoples. Its constitution, which defines health as "a state of complete physical, mental and social well-being and not merely the absence of disease or infirmity," came into force on April 7, 1948, a date now celebrated as World Health Day. The WHO was created to solve the problem of fragmented global health governance, inheriting tasks like epidemic control and quarantine measures from the Health Organization of the League of Nations (set up in 1923) and the International Office of Public Health.
The WHO works through its governing body, the World Health Assembly (WHA), which meets annually to set policy, and its headquarters in Geneva, Switzerland, which oversees six regional offices and 150 country offices. A key mechanism is the International Health Regulations (IHR), a legally binding framework adopted by all 194 member states to prevent and mitigate public health emergencies of international concern (PHEIC). The WHO provides technical assistance, sets international health standards, and coordinates mass campaigns, notably leading to the global eradication of smallpox in May 1980.
The WHO connects directly to the UN Economic and Social Council (ECOSOC) and works with numerous partners like the Global Alliance for Vaccines and Immunization (GAVI). Following the COVID-19 pandemic, the IHR of 2005 were amended in June 2024 to strengthen global health law, including defining a "pandemic emergency" and establishing a Coordinating Financial Mechanism to support low- and middle-income countries. Simultaneously, member states are negotiating a new Pandemic Agreement to improve global coordination and access to vaccines, with a key sticking point being the Pathogen Access and Benefit-Sharing (PABS) system. The WHO also underwent an internal Transformation Agenda to align its work with the Sustainable Development Goals and focus on three "Triple Billion" targets, including universal health coverage and better protection from health emergencies.