The International Atomic Energy Agency (IAEA) - the nuclear watchdog of the United Nations - promotes the peaceful use of atomic energy while trying to make sure that the technology is not used for military purposes.
It has a high-profile role in monitoring compliance with international safeguards, including the 1968 nuclear Non-Proliferation Treaty (NPT). In recent years it has been active in Iran, North Korea and Iraq.
Nobel peace prize judges spoke of the "incalculable" importance of its work in awarding the 2005 prize to the agency and its then director, Mohamed ElBaradei.
The agency also researches the use of atomic energy in such areas as agriculture, industry and medicine. It shares expertise among its members - especially those in the developing world - and sets safety standards.
Iran's nuclear programme goes on despite IAEA pressure
The IAEA advises its members about developing and operating nuclear power stations and disposing of radioactive waste.
It had a big role in the aftermath of Ukraine's Chernobyl nuclear power station disaster in 1986 and is involved in decommissioning the Soviet-era plant.
The IAEA's roots go back to the early 1950s, when rapid advances in nuclear technology were being made and memories of the destruction wrought by the atomic bomb attacks on the Japanese cities of Hiroshima and Nagasaki were fresh.
In 1953 US President Dwight D Eisenhower, mindful of trends which he believed would lead to a nuclear arms race, made his "Atoms for Peace" speech to the UN.
He envisaged a body that would develop the technology along peaceful lines. His vision found form in the IAEA, which began work in 1957 as an autonomous, inter-governmental body under the wing of the UN.
After the 11 September 2001 attacks on the US, Washington backed calls for an increase in the agency's budget and President George W Bush described the IAEA as a key player in the coalition against terrorism. The agency has warned of the dangers of nuclear-related terrorism.
The Bush administration subsequently expressed its dissatisfaction at what it saw as the IAEA's failure to take a tougher line with aspiring nuclear powers such as Iran.
Under Bush's successor, Barack Obama, the US has softened its stance and signalled a readiness to give positive diplomatic engagement with countries such as Iran a chance to work.
However, by 2010 Iran was seen by the US as failing to respond to such overtures, and following a critical IAEA report on Iran published in February, the UN Security Council voted in favour of intensifying sanctions against the country.
- Membership: 145 nations
- Headquarters: Vienna, Austria
- Budget: $398.8m (2009)
- Staff: 2,200 (Secretariat); 670 (in the field)
- Known nuclear-armed states: China, France, India, North Korea, Pakistan, Russia, UK, US (Israel is widely believed to have nuclear arms)
Director-general: Yukiya Amano
The veteran Japanese diplomat Yukiya Amano took over the helm of the agency in December 2009, succeeding Mohamed ElBaradei, who had led the IAEA since 1997.
Mr Amano is seen as taking a tougher line with Iran than his predecessor
Born in 1947, Mr Amano is a law graduate and French speaker. He began his diplomatic career when he joined the Japanese Foreign Ministry in 1972.
He went on to specialise in multilateral disarmament, taking part in the arms control talks that produced the 1995 extension of the Non-Proliferation Treaty (NPT). He became Tokyo's representative to the IAEA in 2005.
Seen as a reserved technocrat, he acknowledged that he was assuming leadership of the organisation at a "stormy" time - with the relationship between the IAEA and Iran having just reached a new low - and pledged to seek to defuse tensions.
However, Mr Amano's first report on Iran, published in February 2010, broke with the more cautious style of his predecessor and for the first time raised concerns that Tehran could be seeking to produce a nuclear warhead for a missile.
He has continued to take a firmer line with Iran than Mr ElBaradei had with a further critical report in late 2010, prompting Tehran to accuse the IAEA of deploying "spies" in the country.
The director-general is assisted by six deputy directors-general. He heads the Secretariat, which is responsible for implementing IAEA programmes.
A 35-member Board of Governors formulates the agency's policies. All IAEA members are part of the General Conference, which meets every year to discuss agency activities and its budget.
The IAEA has no authority to act on its own, but relies on the willingness of nations to cooperate, or on a UN mandate. Its former head, Mohamed ElBaradei, complained that the agency enjoyed only "uneven authority".
The problem became apparent in 2002, when North Korea expelled IAEA inspectors, making it almost impossible for the agency to monitor Pyongyang's nuclear activities.
Meanwhile, Iran's nuclear programme goes on despite increased IAEA pressure for it to suspend its nuclear activities.
Israel, which analysts believe has nuclear warheads, has never signed the Non-Proliferation Treaty and so is not subject to IAEA inspections or sanctions. India and Pakistan, which have acknowledged their possession of nuclear weapons, are also not signatories to the Treaty.
The IAEA has been accused, notably by Pakistan, of restricting the transfer of nuclear know-how to developing countries, hindering their social and economic development.