Vienna is the capital city as well as one of the nine federal countries of Austria.

The city has approximately 1,690,000 inhabitants, the most populous city in the country. About 2.4 million people, more than one quarter of all Austrians, live in the area of Vienna.

Based on the population, Vienna is the tenth largest city in the European Union. With the United Nations Office at Vienna (UNOV), the city is one of the four official headquarters of the United Nations. Other important international organizations based in Vienna are OPEC, OSCE and the International Atomic Energy Agency (IAEA).

The IAEA and the UN have their own building complex, known as UNO City in the center of an urban expansion area near the Danube.