Achaia, sometimes spelled Achaea, was a province of the Roman Empire, consisting of the Peloponnese, Attica, Boeotia, Euboea, the Cyclades and parts of Phthiotis, Aetolia and Phocis. In the north, it bordered on the provinces of Epirus vetus and Macedonia. The region was annexed by the Roman Republic in 146 BC following the sack of Corinth by the Roman general Lucius Mummius, who was awarded the surname "Achaicus". Initially part of the Roman province of Macedonia, it was made into a separate province by Augustus.

The Roman provinces were the administrative regions of Ancient Rome outside Roman Italy that were controlled by the Romans under the Roman Republic and later the Roman Empire. Each province was ruled by a Roman appointed as governor.