Koinon (Greek: Κοινόν, pl. Κοινά, Koina), meaning "common," in the sense of "public," had many interpretations, some societal, some governmental. The word was the neuter form of the adjective, roughly equivalent in the governmental sense to Latin res publica, "the public thing." Among the most frequent uses is "commonwealth," the government of a single state, such as the Athenian.
Frequent in the historical writings is a sense of "league" or "federation" an association of distinct city-states in a sympoliteia. As government of a league, koinon comprised such functions as defense, diplomacy, economics, and religious practices among its member states. The word was carried over to other political associations in mediaeval and modern Greek history.
In Epirus itself there had in ancient times existed the Koinon of the Molossians. There was a Lacedaemonian League, 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.
Some 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
- Acarnanian League (Koinon ton Akarnanon), existing 5th century BC to ca. 30 BC, with interruptions
- Chalcidian League (Koinon ton Chalkideon), existing ca. 430 BC to 348 BC
- Phocian League (Koinon ton Phokeon), existing 6th century BC to 3rd century AD, with interruptions
- Thessalian League (Koinon ton Thessalon), existing 363 BC to 3rd century AD, with interruptions
- League of the Magnetes (Koinon ton Magneton), existing 197 BC to 3rd century AD, with interruptions
- Aenianian League (Koinon ton Ainianon)
- Arcadian League (Koinon ton Arkadon)
- League of the Oeteans (Koinon ton Oitaion)
- Euboean League (Koinon ton Euboieon)
- Epirote League (Koinon Epiroton), existing from ca. 320 BC to ca. 170 BC
- League of the Islanders (Koinon ton Nesioton), existing from ca. 314 BC to ca. 220 BC and 200 BC to 168 BC
- Cretan League under the Roman Empire to the 4th century
- Koinon of Macedonians existing from 3rd century to Roman period
- Lycian League, founded in 168 BC
- League 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