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The Innviertel (literally German for "Inn quarter") is a traditional Austrian region south-east of the Inn river. It forms the western part of the state of Upper Austria and borders the German state of Bavaria. The Innviertel is one of the four traditional "quarters" of Upper Austria, the others being Hausruckviertel, Mühlviertel, and Traunviertel.
The quarter spans the Austrian political districts of Schärding, Ried im Innkreis and Braunau am Inn. Major towns in Innviertel include the district capitals Braunau am Inn, Ried im Innkreis and Schärding as well as Mattighofen and Altheim.
Located within the Alpine foothills, the rural Innviertel is approximately 2250 km² in area and comprises the broad Inn valley, which is largely flat and fertile, and the adjacent undulating landscape in the east, which is rich in granite in the north and coal.
Since the Early Middle Ages the region had belonged to the German stem duchy of Bavaria and was called Innbaiern. Administered from the town of Burghausen, the lands beyond the Inn river for centuries had two important roles: strategically as an eastern defence line against the rising Archduchy of Austria, and economically as arable land for crop farming. In the course of the Bavarian People's Uprising against the occupation by the Habsburg Emperor Joseph I, the short-lived Braunau Parliament convened in 1705, an early occurrence of a parliamentary system in the Holy Roman Empire.
Following the War of the Bavarian Succession and the Treaty of Teschen in 1779 it was ceded to Austria. During the Napoleonic Wars it was once again restored to Bavaria after the 1809 Treaty of Schönbrunn, but finally attached to the Austrian Empire in 1816 according to the Final Act of the Vienna Congress.
Today the Innviertel has about 200,000 people in its towns, villages and hamlets. Its Bavarian roots show in the local German dialect, Innviertlerisch, a Western Central Austro-Bavarian variant similar to the languages spoken in adjacent Lower Bavaria.
Notable people 
The Innviertel is the birthplace of the physicist Anton Zeilinger, of Franz Xaver Gruber, the composer of the Silent Night Christmas carol, of the Schwanthaler family of Baroque sculptors, but also of the SS official Ernst Kaltenbrunner and the conscientious objector Franz Jägerstätter. Adolf Hitler was born at the border town of Braunau am Inn, as well as the diplomat Egon Ranshofen-Wertheimer.