The Tarn (French pronunciation: [taʁn] ⓘ; Occitan: Tarn, Latin: Tarnis, possibly meaning 'rapid' or 'walled in') is a 380.2-kilometre (236.2 mi) long river in the administrative region of Occitania in southern France.

[1] The Tarn runs in a roughly westerly direction, from its source at an elevation of 1,550 m (5,090 ft) on Mont Lozère in the Cévennes mountains (part of the Massif Central), through the deep gorges and canyons of the Gorges du Tarn that cuts through the Causse du Larzac, to Moissac in Tarn-et-Garonne, where it joins the Garonne, 4 km (2.5 mi) downstream from the centre of town.

The Tarn passes through the following departments and towns: The Millau Viaduct, the tallest bridge in the world, carrying the A75 autoroute across the Tarn Gorge near Millau, opened in December 2004.

The Tarn is famous for its brutal floods, which are the most dangerous in Europe along with the Danube.

The floods of March 1930 saw the Tarn rise more than 17 metres (56 feet) above its normal level in Montauban in just 24 hours, with a discharge of 7,000 cubic metres per second (250,000 cu ft/s) (the average discharge of the Rhine is 2,200 cubic metres per second (78,000 cu ft/s); the average discharge of the Nile during the traditional annual flooding before the building of the Aswan Dam was 8,500 cubic metres per second (300,000 cu ft/s); the average discharge of the Mississippi River is 16,200 cubic metres per second (570,000 cu ft/s)).