The Achaens (in Greek old Ἀχαιοί / Akhaioí ) is one of the first Indo-European people to have invaded the Greece, to III, driving out the first inhabitants, the Pélasges thanks to their military supremacy (use of the sword instead of the Poignard, use of the Bronze).

The Argolide becomes their stronghold from where they dominate the remainder of Greece. Homère speaks thus about “Achaens” or “Argiens” to indicate the whole of the Greeks gathered in front of Troy. Their principal centers are the cities of Argos, Tirynthe, Pylos but especially Mycènes, from where the name of civilization mycénienne for the period which goes from the XVII {{E}} to approximately. The fall of the Achaean domination is traditionally allotted to the invasion dorienne, but one thinks from now on that the great invasion was rather a succession of small incursions, spaced in time.

Their ancestor éponyme is Achaïos, wire of Xouthos and of Créüse, half-brother of Ion (ancestor éponyme of the Ioniens).

According to certain specialists, the term hittite Ahhiyawa mentioned in chronicles referred to the Achaens of the Homeric tradition.

In the North-West of Argolide, a mountainous region called " Achaïe" , also holds to have sheltered a flourishing development of Achaean civilization in the cities like Sicyone, Patras, Erymanthe and more in the south, Elis and Olympie.