The Sarmatians (; Ancient Greek: Σαρμάται, romanized: Sarmatai; Latin: Sarmatae [ˈsarmatae̯]) were a large confederation of ancient Eastern Iranian equestrian nomadic peoples of classical antiquity who dominated the Pontic steppe from about the 3rd century BC to the 4th century AD.

Originating in the central parts of the Eurasian Steppe, the Sarmatians were part of the wider Scythian cultures. They started migrating westward around the fourth and third centuries BC, coming to dominate the closely related Scythians by 200 BC. At their greatest reported extent, around 100 BC, these tribes ranged from the Vistula River to the mouth of the Danube and eastward to the Volga, bordering the shores of the Black and Caspian seas as well as the Caucasus to the south.

In the first century AD, the Sarmatians began encroaching upon the Roman Empire in alliance with Germanic tribes. In the third century AD, their dominance of the Pontic Steppe was broken by the Germanic Goths. With the Hunnic invasions of the fourth century, many Sarmatians joined the Goths and other Germanic tribes (Vandals) in the settlement of the Western Roman Empire. Since large parts of today's Russia, specifically the land between the Ural Mountains and the Don River, were controlled in the fifth century BC by the Sarmatians, the Volga–Don and Ural steppes sometimes are called "Sarmatian Motherland."

The Sarmatians in the Bosporan Kingdom assimilated into the Greek civilization, while others were absorbed by the proto-Circassian Meot people, the Alans and the Goths. Other Sarmatians were assimilated and absorbed by the Early Slavs. A people related to the Sarmatians, known as the Alans, survived in the North Caucasus into the Early Middle Ages, ultimately giving rise to the modern Ossetic ethnic group.