Sava also Save (in German: Save; in Hungarian: Száva) is a river in Slovenia, Croatia, Bosnia and Herzegovina and Serbia, a right side tributary of Danube at Belgrade. It is 940 km long and drains 95,720 km² of surface area. In Roman times the river was named Savus. It is often considered a northern boundary of the Balkans.

The Sava has two main sources, both in the north-western, Alpine region of Slovenia. The spring of Sava Dolinka is in Zelenci near Kranjska Gora. The other leg of the river originates as Savica ("little Sava") and then flows into Lake Bohinj , which it leaves as Sava Bohinjka . "Krst pri Savici " is a heroic epic poem written by the most influential Slovenian poet dr. France Prešeren (1800-1849). Both legs of meet at Radovljica , and the river is known as the Sava past that point. Sava flows through the Sava valley .

Its main tributaries, sorted from the source downwards, are the Ljubljanica (flows through Ljubljana), Savinja, Mirna , Krka, Sotla/Sutla, Kupa/Kolpa, Lonja , Orljava , Bosut , Una, Vrbas, Ukrina , Bosna, Tinja , Lukovac , Drina and Kolubara rivers.

Towns on the Sava include Kranj, Zagorje ob Savi, Trbovlje, Hrastnik, Radeče , Sevnica, Krško and Brežice in Slovenia, Zagreb, Sisak, Slavonski Brod and Županja in Croatia, Bosanski Šamac and Brčko in Bosnia and Herzegovia and Sremska Mitrovica, Šabac and Belgrade in Serbia.