Where are the headquarters of IAEA situated?

Concept: International organizations are each anchored to one designated headquarters city, usually fixed by their founding charter or a host-country agreement; several UN-linked nuclear and drug-control bodies cluster in Vienna's 'Vienna International Centre' campus.

Application: The International Atomic Energy Agency (IAEA) was established in 1957, with Vienna, Austria as its headquarters city from the start; the agency moved into its present home, the Vienna International Centre, in 1979, alongside sister bodies such as UNODC and CTBTO.

Cross-check: None of the other listed cities host the IAEA -- distinguishing each below:

• Oslo -- known chiefly as the venue for the Nobel Peace Prize award ceremony, not the seat of any major nuclear or atomic-energy body.

• Geneva -- the base for WHO, WTO, ILO, and the UN Office at Geneva, not the IAEA.

• Copenhagen -- hosts the WHO Regional Office for Europe, not the IAEA.

Hence Vienna is the correct headquarters city of the IAEA.