The Inn (Romansh: En) is a river in Switzerland, Austria and Germany. It is a right tributary of the Danube and is 517 kilometres (321 mi) long. The highest point of its drainage basin is the summit of Piz Bernina, at 4,049 metres (13,284 ft).

The source is located in the Swiss Alps, west of St. Moritz in the Engadin region, which is named after the river (Romansh Engiadina: "garden of the Inn"). Shortly after it leaves its source, the Inn flows through the largest lakes on its course, Lake Sils and Lake Silvaplana. It runs north-eastwards, entering Austria, and from Landeck eastwards through the Austrian state of Tyrol and its capital, Innsbruck (bridge over the Inn), and crosses the border into Bavaria near Kufstein.

On Bavarian territory the river runs northwards and passes the cities of Rosenheim, Wasserburg am Inn, and Waldkraiburg; then it turns east, runs through Mühldorf and Neuötting and is enlarged by two major tributaries, the Alz and the Salzach.

From here to the Danube, it forms the border between Germany (Bavaria) and Austria (Upper Austria). Cities on this last section of the river are Simbach on Inn, Braunau am Inn and Schärding.

Inns are generally establishments or buildings where travelers can seek lodging and, usually, food and drink. They are typically located in the country or along a highway.

Inns in Europe were possibly first established when the Romans built their system of Roman roads two millennia ago. Some inns in Europe are several centuries old. In addition to providing for the needs of travelers, inns traditionally acted as community gathering places.

In Europe, it is the provision of accommodation, if anything, that now separates inns from taverns, alehouses and pubs. The latter tend to supply alcohol (and, in the UK, usually soft drinks and sometimes food), but less commonly accommodation. Inns tend to be grander and more long-lived establishments; historically they provided not only food and lodging, but also stabling and fodder for the traveler's horse(s) and fresh horses for the mail coach. Famous London examples of inns include the George and the Tabard. There is however no longer a formal distinction between an inn and other kinds of establishment. Many pubs use the name "inn", either because they are long established and may have been formerly coaching inns, or to summon up a particular kind of image.

A river is a natural watercourse, usually freshwater, flowing towards an ocean, a lake, a sea, or another river. In a few cases, a river simply flows into the ground or dries up completely before reaching another body of water. Small rivers may also be called by several other names, including stream, creek, brook, rivulet, tributary and rill. There are no official definitions for generic terms, such as river, as applied to geographic features, although in some countries or communities a stream may be defined by its size. Many names for small rivers are specific to geographic location; one example is "burn" in Scotland and northeast England. Sometimes a river is said to be larger than a creek, but this is not always the case, because of vagueness in the language.

Rivers are part of the hydrological cycle. Water within a river is generally collected from precipitation through a drainage basin from surface runoff and other sources such as groundwater recharge, springs, and the release of stored water in natural ice and snowpacks (e.g., from glaciers). Potamology is the scientific study of rivers.