The Mytilenean Debate was an Athenian Assembly concerning reprisals against the city-state of Mytilene, which had attempted unsuccessfully to revolt against Athenian hegemony and gain control over Lesbos during the Peloponnesian War. The debate occurred in 427 BC. In the immediate aftermath of the revolt, the Athenians had decided to execute all Mytilenean men and enslave the women and children, but gathered the next day to reconsider. Thucydides reports the revolt and the resultant debate in book three of his History of the Peloponnesian War, and the opposing viewpoints concerning the warranted retributive justice are reflected in two speeches given by prominent Athenians. The events and speeches serve as an opportunity to explore the political and ideological impact of the war, and provide reflections on democracy and imperial policy.

Mytilene is the capital of the Greek island of Lesbos, and its port. It is also the capital and administrative center of the North Aegean Region, and hosts the headquarters of the University of the Aegean. It was founded in the 11th century BC.