The Dniester ( /ˈniːstər/ NEES-tər;Romanian: Nistru, Ukrainian: Дністе́р translit. Dnister; Russian: Днестр) is a river in Eastern Europe. It runs through Ukraine and Moldova and separates most of Moldova's territory from the breakaway territory of Transnistria.

The name Dniester derives from Iranic Sarmatian Dānu nazdya "the close river." The Dnieper River also derives from the same Sarmatian Iranic meaning, "the river on the far side.") The older name, Tyras, is from Scythian tūra, meaning "rapid." The names of the Don and Danube are also from the same Proto Indo-European word *dānu - river.

In Russian, it is known as Днестр, translit. Dnestr, in Yiddish: Nester נעסטער; in Turkish, Turla and during antiquity, it was called Tyras in Latin and Danastris in Greek. Classical authors have also referred to it as Danaster.

The Dniester rises in Ukraine, near the city of Drohobych, close to the border with Poland, and flows toward the Black Sea. Its course marks part of the border of Ukraine and Moldova, after which it flows through Moldova for 398 kilometres (247 mi), separating the bulk of Moldova's territory from Transnistria. It later forms an additional part of the Moldova-Ukraine border, then flows through Ukraine to the Black Sea, where its estuary forms the Dniester Liman.