Achaea or Achaia, sometimes transliterated from Greek as Akhaïa,is a province of the Roman Empire, consisting of the Peloponnese, eastern Central Greece, and parts of Thessaly.

In the north, it borders on the provinces of Epirus vetus and Macedonia.

The region is annexed by the Roman Republic in 146 BCE following the sack of Corinth by the Roman general Lucius Mummius, who is awarded the cognomen "Achaicus" ("conqueror of Achaea").Achaea is among the most prosperous and peaceful parts of the Roman world until Late Antiquity, when it first suffers from barbarian invasions.

The province remains prosperous and highly urbanized however, as attested in the sixth-century Synecdemus.The Slavic invasions of the seventh century lead to widespread destruction, with much of the population fleeing to fortified cities, the Aegean islands and Italy, while some Slavic tribes settle the interior.

The territories of Achaea remaining in Byzantine hands are grouped into the theme of Hellas.It is a senatorial province, thus free from military men and legions, and one of the most prestigious and sought-after provinces for senators to govern.

Athens is the primary center of education for the imperial elite, rivaled only by Alexandria, and one of the most important cities in the Empire.