The greater part of the country drains into the North Sea via the Rhine, Ems, Weser, and Elbe rivers, which flow in a north-northwest direction. In the east, the Oder River and its tributary, the Neisse River, flow northward into the Baltic Sea and mark the border with Poland. With the exception of the Lahn River, which flows southward before joining the Rhine, most of the tributaries of these rivers flow in a west-to-east or east-to-west direction. In an exception to the south-north pattern of major rivers, the Danube River rises in the Black Forest and flows in a southeasterly direction, traversing Bavaria before crossing into Austria at Passau on the long journey to the Black Sea. The Iller, Lech, Isar, and Inn rivers flow from the south into the Danube and drain the Alpine Foreland.

The Rhine, Germany's longest and most important river, originates in Switzerland, from where it flows into Lake Constance (actually a river basin). At the lake's west end, it begins a long course (800 kilometers) to the Netherlands, at first marking the boundary between Germany and Switzerland and later that between Germany and France. Of the Rhine's three most important tributaries, the Moselle River drains parts of the Rheinish Uplands, the Main drains areas between the Central German Uplands and the Franconian Alb, and the Neckar River drains the area between the Black Forest and the Swabian Alb. Because these rivers keep the Rhine high during the winter and because melting snow in the Alps keeps it high during the spring and summer, the river generally has a high steady flow, which accounts for its being the busiest waterway in Europe.