Koinon (Greek: Κοινόν, pl. Κοινά, Koina), meaning "common" and interpreted as "commonwealth", "league" or "federation" were a number of associations of cities in ancient and early modern Greek history.
The Koinon was a form of government that had existed in various periods in Greek history. It was generally responsible for regulation of defense, diplomacy, economics, and religious practices among its member states.
In Epirus itself there had in ancient times existed the Koinon of the Molossians. There was a Koinon of Laconians, centred on Sparta and its old dominions for a period under Roman rule, a Koinon of the Macedonians, also under Roman rule. In modern Greek history, during the Greek War of Independence, a local self-government termed Koinon was set up in the islands of Hydra, Spetsai and Psara.
The various federations termed Koinon were:
- Ionian League (Koinon Ionon), formed in the 7th century BC
- Koinon of the Aeinautae, recorded on an inscription which was found in Eretria, island Euboea, dated to the 5h century BC
- Chalcidian League (Koinon Chalkideon), existing ca. 430 BC to 348 BC
- Epirote League (Koinon Epiroton), existing from ca. 320 BC to ca. 170 BC
- Koinon of Crete under the Roman Empire to the 4th century
- Koinon of Macedonians existing from 3rd century to Roman period
- Lycian League, founded in 168 BC
- Koinon of Free Laconians, a league of cities in Laconia established by Roman emperor Augustus in 21 BC
- Koinon of the Zagorisians under the Ottoman Empire, 1670–1868
- Mackil, Emily (May 18, 2013). Creating a Common Polity. University of California Press. p. 347. Retrieved October 21, 2014.