The World Health Organization was founded in 1948, and is based in Switzerland.
It is the UN agency responsible for global public health, and has 194 member states.
It is involved in global vaccination campaigns, health emergencies and supporting primary care worldwide.
The WHO aims to "promote health, keep the world safe and serve the vulnerable", and is funded by fees from members - with the amount dependent on population and wealth - and voluntary contributions.
In 2018-19 the US gave more than $400m, around 15% of the WHO's budget. China gave more than any other country, apart from the US - providing around $86m.
Trump, who has branded the WHO "very China-centric", has accused it of not properly assessing the outbreak when it first emerged in Wuhan.
He has claimed that had the agency called out China's "lack of transparency" and not taken the country's assurances at face value, the outbreak could potentially have been contained "with very little death".
On January 14, the WHO tweeted that early Chinese investigations had found "no clear evidence of human-to-human transmission" of the new virus.
But just a week later, the agency released a statement saying that it did appear that there was human-to-human transmission in Wuhan.
Despite the virus emerging in December, WHO experts were only allowed to visit China and investigate the outbreak on 10 February, by which time the country had more than 40,000 cases.
At the end of January, the WHO said travel restrictions were not needed to stop the spread of the coronavirus, which many countries ignored, and there has been some criticism that the agency's guidance on face masks has led to confusion among the public.