The World Health Organization was founded on 7 April 1948

The World Health Organization was founded on 7 April 1948, the day its constitution entered into force after the 26th of the 61 governments that had signed it ratified the document. That date is now marked every year as World Health Day.

It took three years to get there:

• April 1945: at the San Francisco conference that created the United Nations, delegates from Brazil and China proposed an international health organization.
• 22 July 1946: the constitution was signed in New York by representatives of 51 UN members and 10 other nations.
• 7 April 1948: ratifications by the Byelorussian SSR and Mexico reached the threshold set in Article 80, and WHO came into existence as a UN specialized agency.
• 24 June 1948: the first World Health Assembly opened in Geneva, with delegations from 53 of WHO’s 55 member states.

The late joiner with an exit clause

The United States was not among the first 26. Congress authorized membership in a joint resolution that President Truman signed on 14 June 1948, and it came with a condition: because WHO’s constitution has no withdrawal provision, the US reserved the right to leave on one year’s notice. The rest of the membership accepted those terms. The US went on to play a central role in the organization and was historically its largest financial contributor.

The clause sat unused for decades and then mattered. A first withdrawal attempt in 2020 was reversed in 2021, but after a second notice in January 2025 the US formally exited WHO on 22 January 2026, ending a membership that began barely ten weeks after the agency itself.