Osnabrück (German pronunciation: [ɔsnaˈbʁʏk]; Low German: Ossenbrügge; English: Osnaburg) is a city in Lower Saxony, Germany, some 80 km NNE of Dortmund, 45 km NE of Münster, and some 100 km due west of Hanover. It lies in a valley penned between the Wiehen Hills and the northern tip of the Teutoburg Forest. As of December 31, 2010, its population was 164,119, making it the third-largest city in Lower Saxony.

Osnabrück developed as a marketplace next to the bishop's see founded by Charlemagne, king of the Franks, 780. Some time before 803, the city became seat of the Prince-Bishopric of Osnabrück. Although the precise date is uncertain, Osnabrück is likely the oldest bishopric in Lower Saxony.

In the year 804 Charlemagne was said to have founded the Gymnasium Carolinum in Osnabrück. This date would make it the oldest German Gymnasium but the charter date is disputed by historians, some of whom believe it could be a forgery.

In 889 the town was given merchant, customs, and coinage privileges by King Arnulf of Carinthia. It is first mentioned as a "city" in records in 1147. Shortly after in 1157, Emperor Frederick Barbarossa granted the city fortification privileges (Befestigungsrecht). Part of the medieval fortification, most of the towers are still visible in the city. Osnabrück became a member of the Hanseatic League in the 12th century, as well as a member of the Westphalian Federation of Cities.