Parthia is a region of north-eastern Iran, best known for having been the political and cultural base of the Arsacid dynasty, rulers of the Parthian Empire.

The name "Parthia" is a continuation from Latin Parthia, from Old Persian Parthava, which was the Parthian language self-designator signifying "of the Parthians" who were an Iranian people.

Parthia roughly corresponds to the western half of Khorasan region in northeastern Iran. It was bordered by the Kopet Dag mountain range in the north and the Dasht-e-Kavir desert in the south. It bordered Media on the west, Hyrcania on the north west, Margiana on the north east, and Aria on the south east.

During Arsacid times, Parthia was united with Hyrcania as one administrative unit, and that region is therefore often (subject to context) considered a part of Parthia proper.

As the region inhabited by Parthians, Parthia first appears as a political entity in Achaemenid lists of governorates ("satrapies") under their dominion. Prior to this, the people of the region seem to have been subjects of the Medes, and 7th century BC Assyrian texts mention a country named Partakka or Partukka (though this "need not have coincided topographically with the later Parthia").