International cooperation to control the cross-border spread of infectious disease began with the first International Sanitary Conference in Paris in 1851, which sought to standardize quarantine regulations against cholera, plague, and yellow fever. In the early twentieth century, permanent bodies emerged, including the Pan American Sanitary Bureau in 1902, the Paris-based Office International d'Hygiène Publique (OIHP) in 1907, and the Health Organization of the League of Nations in 1920. Following the Second World War, during the 1945 United Nations Conference on International Organization in San Francisco, delegates from Brazil and China proposed establishing a single, unified global health agency.¹⁵

On 15 February 1946, the United Nations Economic and Social Council instructed the Secretary-General to convene a conference to frame the agency's constitution. Following preparatory meetings in Paris, the International Health Conference met in New York City from 19 June to 22 July 1946. Representatives of 51 United Nations member states and 10 other nations signed the Constitution of the World Health Organization on 22 July 1946. The constitution entered into force on 7 April 1948, when the twenty-sixth member state ratified it, a date subsequently observed annually as World Health Day. The agency formally began operations on 1 September 1948, absorbing the assets, personnel, and duties of the OIHP and the League of Nations Health Organization. Canadian psychiatrist Brock Chisholm served as its first Director-General from 1948 to 1953.¹⁶

During the tenure of its second Director-General, Marcolino Gomes Candau of Brazil (1953–1973), the WHO expanded its field operations and launched ambitious vertical disease eradication campaigns. In 1955, the World Health Assembly initiated the Global Malaria Eradication Programme, relying heavily on the insecticide DDT and antimalarial drugs; while the campaign eliminated malaria in many developed and subtropical nations, it failed to achieve global eradication and was eventually reoriented toward control. In 1958, upon a proposal from the Soviet Union, the WHO initiated its global smallpox eradication effort, which was intensified in 1967 with dedicated funding, ring vaccination strategies, and surveillance. In 1969, the agency also adopted the International Health Regulations to govern disease reporting at borders.

Under Danish physician Halfdan Mahler, who served as Director-General from 1973 to 1988, the WHO shifted its emphasis from vertical, disease-specific interventions toward horizontal health system strengthening.¹⁷ On 8 May 1980, the World Health Assembly officially declared smallpox eradicated, the first human disease eliminated by deliberate intervention. Two years earlier, in September 1978, the WHO and UNICEF jointly convened the International Conference on Primary Health Care in Alma-Ata, Kazakh Soviet Socialist Republic.¹⁸ The resulting Alma-Ata Declaration identified comprehensive primary health care as the cornerstone for achieving the goal of "Health for All by the Year 2000".¹⁹

In 1988, the Assembly launched the Global Polio Eradication Initiative and elected Hiroshi Nakajima of Japan as Director-General (1988–1998).²⁰ During the 1990s, the rise of the HIV/AIDS pandemic, the resurgence of tuberculosis, and the growing role of the World Bank and bilateral donors challenged the WHO's centrality in global health. Former Norwegian Prime Minister Gro Harlem Brundtland, serving from 1998 to 2003, sought to restore the agency's political standing by prioritizing tobacco control, establishing the Commission on Macroeconomics and Health, and fostering public-private partnerships such as Gavi, the Vaccine Alliance, and the Global Fund to Fight AIDS, Tuberculosis and Malaria. She was succeeded by Lee Jong-wook of South Korea (2003–2006), who launched the "3 by 5" initiative to expand antiretroviral treatment for HIV/AIDS before dying in office in May 2006. After an interim period under Anders Nordström of Sweden, Margaret Chan of China served from 2007 to 2017, overseeing responses to the 2009 H1N1 influenza pandemic and the 2014–2016 West African Ebola epidemic.²¹ In May 2017, the Assembly elected former Ethiopian health and foreign minister Tedros Adhanom Ghebreyesus as the first African Director-General, re-electing him in May 2022.²²

The WHO is governed by its member states through two principal bodies: the World Health Assembly and the Executive Board. Following the withdrawal of the United States in January 2026, membership stood at 193 member states, comprising all United Nations member states except Liechtenstein and the United States, alongside two non-UN member states from the Pacific, the Cook Islands and Niue.²³ Territories that are not responsible for the conduct of their international relations may be admitted as associate members; Puerto Rico and Tokelau hold associate membership. The Holy See, the Sovereign Military Order of Malta, Palestine, and several intergovernmental bodies participate as observers.

The World Health Assembly (WHA) is the supreme decision-making body of the organization. It convenes annually in May in Geneva, attended by delegations from all member states, typically led by national ministers of health.²⁴ The Assembly determines the policies of the organization, approves the biennial programme budget, reviews financial reports, and elects the Director-General every five years.²⁵ Under Articles 19, 21, and 22 of the WHO Constitution, the WHA holds the authority to adopt legally binding conventions and international regulations on sanitary and quarantine requirements, disease nomenclature, and standards for pharmaceutical products.²⁶

The Executive Board is composed of 34 individuals who are technically qualified in the field of health, each designated by a member state elected to do so by the World Health Assembly. Member states are elected for three-year terms according to an equitable geographical distribution across the WHO's six regions. The Board meets at least twice a year, with its main meeting in January or February to agree upon the agenda and resolutions for the forthcoming Assembly, and a shorter administrative session in May immediately following the Assembly.²⁷ Its core mandate is to give effect to the decisions and policies of the WHA, advise it, and facilitate its work.

The Secretariat carries out the day-to-day technical and administrative functions of the agency and is headed by the Director-General, who is nominated by the Executive Board and appointed by the Assembly for a five-year term, renewable once. The WHO headquarters in Geneva, housed in a campus designed by Swiss architect Jean Tschumi and inaugurated in 1966, employs approximately 2,400 staff out of a global workforce of roughly 9,000 to 10,000 personnel.²⁸ Alongside its Geneva headquarters, the agency maintains specialized outposted centres, including the International Agency for Research on Cancer (IARC) in Lyon, France; the WHO Centre for Health Development in Kobe, Japan; the Global Service Centre in Kuala Lumpur, Malaysia; the WHO Hub for Pandemic and Epidemic Intelligence in Berlin, Germany; and the WHO Academy in Lyon.²⁹

The WHO operates on a two-year (biennial) budgetary cycle financed through two primary channels: assessed contributions and voluntary contributions.³¹³² Assessed contributions are mandatory membership dues paid by member states, calculated according to a scale of assessments approved by the United Nations General Assembly that accounts for each country's gross domestic product and population size. Voluntary contributions consist of additional funds provided by member states, intergovernmental organizations such as the European Union, philanthropic foundations, development banks, and private entities.

In the agency's early decades, assessed contributions funded the vast majority of its regular budget. Beginning in the 1980s, member states imposed a policy of zero real growth—and later zero nominal growth—on assessed dues, causing mandatory contributions to shrink as a proportion of total expenditure. By the 2020–2021 biennium, assessed contributions accounted for only 16 percent of the approved programme budget, while more than 80 percent came from voluntary contributions.³³ Furthermore, roughly 87 percent of those voluntary contributions were "specified" or earmarked by donors for particular diseases, projects, or geographic areas, leaving the WHO leadership with limited flexible funding to allocate toward core functions such as health system strengthening, non-communicable diseases, and emergency preparedness.

To address the structural vulnerability of relying on a narrow base of earmarked donations, the World Health Assembly adopted recommendations from its Sustainable Financing Working Group in May 2022. Member states committed to gradually increasing their assessed contributions to cover 50 percent of the WHO's base budget by the 2030–2031 biennium. As part of this transition, the Assembly approved a 20 percent increase in assessed dues for the 2024–2025 budget and a second 20 percent increase in May 2025 for the 2026–2027 budget. The agency also established the WHO Foundation in 2020 to solicit private and philanthropic donations and launched its first Investment Round in May 2024 to secure multi-year flexible funding for its Fourteenth General Programme of Work (2025–2028). Despite these reforms, the suspension of funding from the United States in 2025 forced the WHA to downsize the 2026–2027 base programme budget by 22 percent, from an initially planned $5.3 billion to approximately $4.2 billion.

A foundational pillar of the WHO's mandate is its normative work: establishing international nomenclatures, treatment guidelines, regulatory standards, and legal frameworks that member states adopt into national law and clinical practice. Since 1948, the agency has maintained the International Statistical Classification of Diseases and Related Health Problems (ICD), the global standard for diagnostic coding and the reporting of mortality and morbidity statistics. The eleventh revision (ICD-11), adopted by the World Health Assembly in 2019, officially came into effect in January 2022 as a fully digital, multilingual classification system.

Since 1977, the WHO has published the Model List of Essential Medicines, updated every two years by an expert committee to identify medications that satisfy the priority healthcare needs of populations based on efficacy, safety, and cost-effectiveness.³⁴ In 2007, it added a dedicated Model List of Essential Medicines for Children. By 2026, more than 150 countries used the WHO Model Lists—in their 24th adult edition and 10th pediatric edition as of September 2025—as the basis for national medicine procurement, insurance reimbursement, and domestic manufacturing. To combat antimicrobial resistance, the list incorporates the AWaRe (Access, Watch, Reserve) classification framework to guide antibiotic stewardship. Complementing this work, the WHO Prequalification Programme, established in 2001, evaluates the quality, safety, and efficacy of vaccines, medicines, and diagnostics to guide bulk purchasing by agencies such as UNICEF, the Global Fund, and Gavi.

The WHO has also exercised its constitutional treaty-making powers to address non-communicable health threats. In May 2003, the World Health Assembly unanimously adopted the WHO Framework Convention on Tobacco Control (FCTC), the first treaty negotiated under Article 19 of the WHO Constitution.³⁵³⁶ Entering into force in February 2005, the FCTC obligates its parties to implement demand- and supply-reduction measures, including tobacco taxation, health warnings on packaging, bans on tobacco advertising, and protections against exposure to secondhand smoke. In collaboration with the Food and Agriculture Organization (FAO), the WHO also administers the Codex Alimentarius Commission, established in 1963 to set international food safety standards, and publishes the Guidelines for Drinking-water Quality.

Alongside its normative work, the WHO coordinates international efforts to prevent, control, and eradicate communicable diseases and responds to acute public health emergencies. Following the eradication of smallpox in 1980, the Global Polio Eradication Initiative—a partnership involving the WHO, Rotary International, the US Centers for Disease Control and Prevention, UNICEF, and later Gavi and the Gates Foundation—reduced global polio cases by more than 99 percent, certifying the eradication of wild poliovirus type 2 in 2015 and type 3 in 2019, while continuing campaigns against wild poliovirus type 1 in Afghanistan and Pakistan.³⁷³⁸ Through the Expanded Programme on Immunization, established in 1974, the organization coordinates global childhood vaccination schedules. It also leads programmes targeting HIV/AIDS, tuberculosis, malaria—recommending the first malaria vaccines, RTS,S and R21, in the early 2020s—and 20 neglected tropical diseases such as trachoma, dracunculiasis, and human African trypanosomiasis.³⁹

The legal cornerstone of the WHO's emergency work is the International Health Regulations (IHR). Originally adopted as the International Sanitary Regulations in 1951 and renamed in 1969, the IHR were substantially revised in 2005 following the 2002–2004 severe acute respiratory syndrome (SARS) outbreak. Entering into force in June 2007, the IHR (2005) legally bound 196 states parties to develop core surveillance and response capacities and to notify the WHO within 24 hours of any event that might constitute a Public Health Emergency of International Concern (PHEIC).⁴⁰⁴¹ Under the regulations, the Director-General, advised by an Emergency Committee of international experts, holds the sole authority to declare a PHEIC and issue temporary recommendations on health measures, travel, and trade.

Between 2009 and 2026, the WHO declared a PHEIC nine times: the 2009–2010 H1N1 influenza pandemic; the ongoing declaration for poliomyelitis issued in May 2014; the 2014–2016 Ebola epidemic in West Africa; the 2016 Zika virus epidemic in the Americas; the 2019–2020 Kivu Ebola epidemic in the Democratic Republic of the Congo (DRC); the COVID-19 pandemic from January 2020 to May 2023; the global clade II mpox outbreak from July 2022 to May 2023; the clade I mpox epidemic centered in Central Africa from August 2024 to 2026; and the May 2026 declaration for an Ebola Bundibugyo outbreak in the DRC and Uganda.⁴² Following criticism of its delayed operational response to the 2014 West African Ebola outbreak, the World Health Assembly established the WHO Health Emergencies Programme (WHE) in 2016, equipping the agency with an operational arm, a Contingency Fund for Emergencies, and a standardized incident management system to deploy medical teams and supplies directly into crisis zones.⁴³

Because the WHO is an intergovernmental organization dependent on the cooperation and financial support of sovereign member states, it lacks the authority to compel governments to accept inspectors, share epidemiological data, or comply with its recommendations. This structural limitation has repeatedly placed the agency at the center of geopolitical and public health controversies.⁴⁴ During the 2009 H1N1 influenza pandemic, critics and a Council of Europe parliamentary inquiry accused the organization of overstating the severity of the virus and failing to disclose potential conflicts of interest among scientific advisers who had ties to pharmaceutical manufacturers producing antiviral drugs and vaccines.

Conversely, independent review panels faulted the WHO for reacting too slowly to the 2014 Ebola outbreak in Guinea, Liberia, and Sierra Leone, waiting until August 2014—nearly five months after international medical charities warned of an unprecedented epidemic—to declare a PHEIC. Reviewers attributed the delay to bureaucratic division between the Geneva headquarters and the Regional Office for Africa, budget cuts to emergency response units following the 2008 financial crisis, and reluctance to offend affected governments concerned about economic damage to trade and tourism.⁴⁵

During the COVID-19 pandemic, the WHO faced intense scrutiny over its relationship with China and the timing of its technical guidance. Critics, most prominently the United States government, accused the agency and Director-General Tedros of being overly deferential to Beijing in early 2020, citing the WHO's initial repetition of Chinese assurances that there was no clear evidence of human-to-human transmission and its opposition to early travel restrictions. Scientific critics also faulted the agency for taking months to formally acknowledge the major role of airborne aerosol transmission of SARS-CoV-2 and for failing to prevent vaccine hoarding by wealthy nations despite establishing the COVAX facility. Defenders of the organization, along with the Independent Panel for Pandemic Preparedness and Response, noted that the WHO declared a PHEIC on 30 January 2020 when fewer than 100 cases and no deaths had been reported outside China, and argued that the agency possessed no legal power under the IHR to verify state-reported data independently or force access for origins investigations without host-country consent.

The organization has also contended with diplomatic disputes and internal governance scandals. After the United Nations passed Resolution 2758 in 1971 recognizing the People's Republic of China as the sole legitimate representative of China, Taiwan (Republic of China) lost its seat at the WHO. From 2009 to 2016, Taiwan was invited to attend the World Health Assembly as an observer under the name "Chinese Taipei," but Beijing blocked invitations from 2017 onward following the election of Taiwanese administrations it opposed, prompting criticism from Western governments that Taiwan's exclusion created a gap in global disease surveillance. Internally, an independent commission reported in September 2021 that 21 of 83 alleged perpetrators of sexual exploitation and abuse during the 2018–2020 Ebola response in the DRC were WHO employees or contractors, leading to management reforms and victim support funds. In early 2023, the Executive Board removed the Regional Director for the Western Pacific, Takeshi Kasai, following an internal investigation into allegations of racist and abusive workplace behavior.

In the aftermath of the COVID-19 pandemic, member states initiated two parallel negotiations to overhaul the international legal architecture for health emergencies. On 1 June 2024, at the 77th World Health Assembly, member states adopted a package of amendments to the International Health Regulations (2005), which formally entered into force on 19 September 2025 for all states parties except 11 countries that registered rejections.⁴⁶ The amended regulations introduced a new highest tier of alert—a "pandemic emergency"—designed to trigger coordinated international mobilization when a communicable disease risk escalates beyond a standard PHEIC to threaten widespread health system and societal disruption. The amendments also mandated the creation of National IHR Authorities and established a Coordinating Financial Mechanism to help developing countries build core surveillance capacities and access medical countermeasures.

On 20 May 2025, during the 78th World Health Assembly, member states adopted the WHO Pandemic Agreement by a vote of 124 in favor, zero opposed, and 11 abstentions. Negotiated over more than three years, it became only the second legally binding treaty adopted under Article 19 of the WHO Constitution, establishing commitments on "One Health" zoonotic surveillance, geographic diversification of pharmaceutical manufacturing, and healthcare workforce protection. However, opening the treaty for formal signature and ratification was made contingent upon finalizing its most contested component: Article 12, which establishes a Pathogen Access and Benefit-Sharing (PABS) system requiring pharmaceutical manufacturers that use shared genetic sequence data or physical pathogen samples to allocate a percentage of their real-time production of vaccines, therapeutics, and diagnostics to the WHO for distribution to developing nations during emergencies.⁴⁷⁴⁸ At the 79th World Health Assembly in May 2026, with developed and developing nations still divided over commercial obligations and intellectual property, delegates extended negotiations on the PABS Annex under an Intergovernmental Working Group toward a special session or the 80th Assembly in May 2027.

These legal reforms coincided with a major geopolitical and financial rupture: the departure of the agency's largest historical single-country donor. During his first presidency in July 2020, US President Donald Trump submitted a one-year notice of withdrawal from the WHO, which President Joe Biden rescinded on 20 January 2021 before it took effect.⁴⁹⁵⁰⁵¹ Upon returning to office on 20 January 2025, Trump signed Executive Order 14155, immediately halting all US assessed and voluntary funding to the agency, recalling US personnel embedded with the WHO, and ceasing US participation in negotiations on the Pandemic Agreement and IHR amendments. Relying on a unique reservation attached by the US Congress when joining the organization in 1948 that permitted withdrawal upon a one-year notice, the United States formally exited the WHO on 22 January 2026, though legal disputes persisted over more than $133 million in unpaid US assessed dues for 2024 and 2025.

The loss of United States contributions, which had historically provided roughly 15 to 18 percent of the agency's total funding, created a nearly $1 billion shortfall for the 2026–2027 biennium. In response, the WHO implemented a sweeping institutional restructuring in 2025 and 2026, consolidating its Geneva headquarters from 11 divisions to 6, reducing the number of departments from 67 to 36, and cutting its total global workforce by nearly 10 percent. By late 2026, member states also began the formal process to elect a successor to Director-General Tedros Adhanom Ghebreyesus ahead of the conclusion of his second and final term in 2027.