The World Health Organization (WHO) has played a key role in fighting disease around the globe for more than 50 years.
The WHO was established in 1948
But rarely has it been the focus of such sustained media and public attention than in recent weeks.
The outbreak of the deadly Sars virus has seen the WHO come under the spotlight like never before.
Its scientists, doctors and officials are at the forefront of what is now a global battle against this mystery virus.
Sars has so far infected thousands of people and claimed the lives of hundreds more in over 25 countries around the world.
The WHO has spearheaded the global offensive against the virus since the start. Dr Carlo Urbani, one of its communicable diseases experts, was the first to identify the virus. It subsequently killed him.
At the end of March, officials alerted the world to the Sars threat. In early April, it recruited scientists from around the world to try to identify the cause of Sars.
Its officials quickly moved into positions on the frontline in China - where the virus is believed to have originated - in an attempt to fight Sars head on and stop it from spreading.
In recent days, it has stepped up its efforts to contain the virus warning people against travelling to disease hot spots around the world, including Beijing, Hong Kong and Toronto.
It was an unprecedented and controversial move but one officials at WHO headquarters in Geneva insist was necessary.
That decision has sparked criticism, not least in Toronto, where officials said the travel alert was unnecessary. The WHO has now lifted that warning.
The WHO was established in 1948 as an agency of the United Nations to improve health around the globe. Close to 200 countries are now members.
It is governed by the World Health Assembly, consisting of representatives of the entire membership, which meets at least once a year; an executive board elected by the assembly; and a secretariat headed by a director-general.
Key WHO facts
Established in 1948
Its headquarters are in Geneva, Switzerland
Almost every country in the world is a member
Credited with eliminating smallpox
It has regional organisations in Africa, the Eastern Mediterranean, south-east Asia, Europe, the western Pacific, and the Americas.
It has made notable strides in tackling a range of serious diseases, including smallpox, polio, leprosy, cholera and tuberculosis.
Its efforts have undoubtedly helped to save hundreds of thousands of lives around the world.
"The WHO has been behind some crucial initiatives over the past 50 years," says Mike Rowson of Medact, a non-governmental organisation which aims to focus attention on barriers to better health.
The UN agency was originally established to strengthen national health systems and to help prevent and control epidemics. Inevitably, its focus has evolved over the past 50 years.
In the 1950s, the organisation was predominantly focused on tackling diseases, including malaria and smallpox which was successfully eradicated.
By the 1970s, it had turned its attention to improving health services in developing countries and tackling health inequalities.
In the 1980s, in line with the political priorities of the time officials concentrated on tackling healthcare funding around the world.
During the 1990s, the agency came in for criticism and was accused of taking its eye off the ball.
It was facing "competition" from other bodies including the World Bank, which were beginning to play a much bigger role in international health and according to some were working more effectively.
Its response to the new global threat of HIV also came under fire amid concern that its response was too slow, not least in parts of the world hit hardest by the virus.
We need an organisation like the World Health Organization
Professor Gill Walt,
London School for Hygiene and Tropical Medicine
In recent years, the WHO has concentrated its energies once again on fighting diseases and has stepped up efforts to establish more effective vaccination programmes.
Nevertheless, many believe it could be doing more. Some non-governmental organisations accuse it of failing to stand up to the pharmaceutical industry to secure cheap drugs for people living in the developing world.
Others criticise its attempts to tackle underlying causes of ill-health, such as poverty and access to medical services.
"Ten million children die needlessly every year because of poverty and lack of access to services," says Mike Rowson. "The WHO cannot solve this problem on its own but it could push governments to address these underlying problems."
One of the WHO's major problems throughout its 50-year history has been its limited budget.
Its global operations are funded by a $1bn budget. Many other agencies with more focused remits spend substantially more.
Others have accused it of being overly bureaucratic. Some 3,500 people make up its secretariat.
The incoming director general has pledged to reduce spending on the secretariat and to devolve more power and presumably money to the frontline.
Nevertheless, the Sars outbreak and subsequent global battle against the virus has highlighted the unique strengths of an agency with over 50 years experience and uniquely close contacts with practically every government in the world.
"We need an organisation like the World Health Organization," says Gill Walt, professor of international health policy at the London School for Hygiene and Tropical Medicine.
Sars may also strengthen the WHO's hand when it comes to securing additional funds in the months and years ahead.
But above all, it should send a clear message to governments around the world - namely that no other agency could spearhead a global fight of this kind.