The Jiu is a river of southern Romania. It is formed near Petroşani by the junction of headwaters Jiul de Vest and Jiul de Est.

It flows southward through the Romanian counties Hunedoara, Gorj and Dolj before flowing into the Danube a few kilometers upstream from the Bulgarian city of Oryahovo, 331 kilometers from its sources. It has a basin of 10,070 km².

The upper Jiu Valley, around Petroşani and Lupeni, is Romania’s principal coal mining region.

The following towns are situated along the river Jiu, from source to mouth: Petroşani (Jiul de Est), Lupeni (Jiul de Vest), Bumbeşti-Jiu, Turcineşti, Târgu Jiu, Filiaşi, Craiova.

The following rivers are the major tributaries to the river Jiu: Gilort,  Jiul de Est, Jiul de Vest and Motru.