The Tisza, Tysa or Tisa, is one of the major rivers of Central and Eastern Europe. Once, it was called "the most Hungarian river" because it flowed entirely within the Kingdom of Hungary. Today, it crosses several national borders.

The Tisza begins near Rakhiv in Ukraine, at the confluence of the White Tisa and Black Tisa, which is at coordinates 48°4′29″N 24°14′40″E (the former springs in the Chornohora mountains; the latter in the Gorgany range). From there, the Tisza flows west, roughly following Ukraine's borders with Romania and Hungary, then shortly as border between Slovakia and Hungary, later into Hungary, and finally into Serbia. It enters Hungary at Tiszabecs. It traverses Hungary from north to south. A few kilometers south of the Hungarian city of Szeged, it enters Serbia. Finally, it joins the Danube near the village of Stari Slankamen in Vojvodina, Serbia.

The Tisza drains an area of about 156,087 km² (60,266 sq mi) and has a length of 966 km (600 mi) Its mean annual discharge is seasonally 792 m³/s (28,000 cu ft/s) to 1,050 m³/s (37,000 cu ft/s). It contributes about 13% of the Danube's total runoff.

Attila the Hun is said to have been buried under a diverted section of the river Tisza.