The Aetolian (or Aitolian) League (Ancient Greek: Κοινὸν τῶν Αἰτωλῶν) was a confederation of tribal communities and cities in ancient Greece centered in Aetolia in Central Greece. It was probably established during the late Classical or the early Hellenistic era. Two annual meetings were held at Thermon and Panaetolika. The league occupied Delphi and steadily gained territory after its victory there against the Gauls in 279 BC. By the end of the 3rd century BC, it controlled the whole of central Greece with the exception of Attica, Euboea, Boeotia and northwestern Acarnania. At its peak, the league's territory included Locris, Phocis, Doris, Malis, Dolopia, Achaia Phthiotis, Ainis, Oetaea, Ambracia and parts of Acarnania. In the latter part of its power, certain Greek city-states out of central Greece joined the Aetolian League such as the Arcadian cities of Mantineia, Tegea, Phigalia and Kydonia on Crete.
During the classical period the Aetolians were not highly regarded by other Greeks, who considered them to be semi-barbaric and reckless. However, during the Hellenistic period, they emerged as a dominant state in central Greece and expanded by annexing several Greek city-states to the League after their victory against the Gauls in 279 BC. Their League had a complex political and administrative structure. The Aetolian League fought against Macedon and the Achaean League in the Social War (220-217 BC), allied with Rome in the First Macedonian War and Second Macedonian War, but then fought against the Romans in an alliance with the Seleucid empire in the Aetolian War before losing its independence to Rome.