INN, a right bank tributary of the Danube. It rises in a small lake under Piz Longhino, in the Swiss canton of the Grisons. After flowing for 55 m. through the Engadine, it enters Austria at Martinsbruck, and continues as a swift mountain stream along the Inn Thal as far as Innsbruck where it enters the broader Unter Inn Thal. At Rosenheim it leaves the limestone zone of north Tirol and enters the plateau of Upper Bavaria, across which it flows to join the Danube at Passau. Its chief tributary is the Salzach on which stands the town of Salzburg. (See DANUBE.)