The Tanaro (Italian pronunciation: [ˈtaːnaro]; Piedmontese: Tane [ˈtɑne]; Ligurian: Tànau [ˈtana(ɹ)u]; Latin: Tanarus) is a 276-kilometre (171 mi) long river in northwestern Italy.

This mountain straddles the French département of Alpes-Maritimes, the Piedmontese province of Cuneo and the Ligurian province of Imperia and marks the juncture of the watersheds between three drainage basins: Tanaro itself; Roya (Italian: Roia), which rises in France but enters the sea at Ventimiglia; and Argentina, which flows into the Ligurian Sea at Taggia.

The main tributaries to the Tanaro are the Stura di Demonte, the Pesio, the Ellero and the Borbore from the left and the Bormida and the Belbo from the right.

Although the river has an Alpine origin, which is unique among the Po’s right-side tributaries, the Ligurian Alps are of an insufficient elevation and too close to the sea to allow for the formation of snow fields or glaciers large enough to provide a steady source of water during the summer.

The seasonal regime of the river is therefore more typical of an Apennine stream, with a maximum discharge that can reach 1,700 cubic metres per second (60,000 cu ft/s), in spring and autumn and a very low rate of flow in the summer.