With a length of 2,845 km, the Danube is the second-longest river in Europe after the Volga. On almost 2,415 km (from Kelheim to Sulina) the river is navigable for international cargo transport. On its way from the Black Forest (Germany) to its mouth in the Black Sea (Romania and Ukraine), the Danube passes by or through ten riparian states, which makes it the most international river in the world.

Since the opening of the Main-Danube Canal in 1992, 14 European countries are directly linked by inland waterways on the Rhine-Main-Danube axis. The total length of this waterway axis from the mouth of the Danube in the Black Sea to the mouth of the Rhine in the North Sea is 3,504 km. The Rhine-Main and the Danube river basins are connected by the 171 km long Main-Danube Canal.

On the international inland waterways Danube and Rhine navigation is exempt from charges. Fees must be paid for navigating on the Main-Danube Canal (Germany) and the Danube-Black Sea Canal (Romania), as these are national waterways which are not included in the Belgrade Convention of 1948. As stipulated by all Danube riparian states in the Convention Regarding the Regime of Navigation on the Danube, navigation on the Danube is free and open for all vessels of commerce sailing under the flags of all states.