For other uses, see Main (disambiguation).

The Main is a river in Germany, 524 km in length, and one of the more voluminous tributaries of the Rhine river. It flows through the Bundesländer Bavaria and Hessen. Its catchment basin competes with the Danube for water; as a result, much of its boundaries are identical with the European Watershed .

The Main is formed near Kulmbach by the joining of its two headstreams, the Red Main and the White Main. The former rises from the Frankish Alb, is 50 km in length, and runs through Creussen and Bayreuth. The latter's source is located in the mountains of the Fichtelgebirge; it is 41 km in length. Major tributaries of the Main are the Regnitz, the Frankish Saale, the Tauber, and the Nidda.

The largest city along the Main is Frankfurt am Main (ford of the Franks). After the junction of its headstreams, the Main passes the following towns and cities: Burgkunstadt , Lichtenfels , Staffelstein , Hallstadt , Zeil , Hassfurt , Schweinfurt, Volkach, Kitzingen, Marktbreit, Ochsenfurt , Würzburg, Karlstadt, Gemünden , Lohr , Marktheidenfeld , Wertheim, Miltenberg, Obernburg , Aschaffenburg, Seligenstadt , Hanau, Offenbach, Frankfurt, Hattersheim , Flörsheim , Rüsselsheim. By the time it flows into the Rhine opposite Mainz it is a formidable river.

Extensive works have made the Main navigable for river shipping from its mouth at the Rhine via the Rhine-Main-Danube Canal and the highly regulated Altmühl river, all the way to the Danube.