(432–348 BC), confederacy of the Greek cities of Chalcidice in northeastern Greece directed at first against Athens and later, after the defeat of Athens in the Peloponnesian War, against encroachment by Macedonia. Founded by Olynthus as a league with complete equality and identical citizenship, commerce, and marriage laws among the member states, it included almost all the cities on the Macedonian coast by 382 BC.

Sparta, initially sending a small force to the Chalcidice peninsula to protect Acanthus and Apollonia, which were resisting forcible incorporation, soon interpreted the league as a threat to its aspirations in Greece and starved Olynthus into surrender in 379 BC, dissolving the confederation. In a few years, however, the Chalcidian cities again federated. In 349, after Olynthus had become suspicious of the expansionist designs of his ally Philip II of Macedon, the cities entered an alliance with Athens, only to be conquered by Philip in 348.