The Wien is a river that flows through the city of Vienna. It is 34 kilometers long, of which 15 are within the city. Its drainage basin covers an area of 230 km², both in the city and in the neighboring Wienerwald.

Nomenclature: in German, the river is colloquially called the '"Wienfluss". Since English uses the name "Vienna" for what in German is called "Wien", in English the river is sometimes called the "Vienna River".

The Wien has its source in the western Wienerwald near Rekawinkel and its mouth at the eastern end of the city center of Vienna, next to the Urania , where it flows into the Donaukanal ("Danube canal"), a branch of the Danube.

Within the city limits, the riverbed consists almost entirely of concrete, which was installed between 1895 and 1899 in order to stop the devastating floods--sometimes accompanied by cholera--which the river had regularly caused before that time. At the same time, the Stadtbahn ("city railway") was built, which makes use of the concrete riverbed and is only separated from the river by a wall. It is part of Vienna's U-Bahn system today.

The Wien is subject to huge variations in flow. In its headwaters in the Wienerwald, the soil is underlain by sandstone. Because of this, during heavy rain the soil quickly saturates, resulting in substantial runoff. Thus the flow of the Wien can quickly increase from a creek-like 200 liters per second to (in the heaviest rains or during the spring snowmelt in the Wienerwald), 450,000 liters per second, a ratio of over 2000.

Along the course of the river, the Naschmarkt and the Theater an der Wien can be found. Much of the river is covered over in the city, particularly in front of Schönbrunn palace, at the Meidling and Naschmarkt neighborhoods and around the Karlsplatz near the city center.