The Athenian coup of 411 BC was the result of a revolution that took place during the Peloponnesian War between Athens and Sparta. The coup overthrew the democratic government of ancient Athens and replaced it with a short-lived oligarchy known as the Four Hundred.

In the wake of the financial crisis caused by the failed Sicilian Expedition of the Athenian military in 413 BC, some high-status Athenian men, who had disliked the broad-based democracy of the city-state for a long time, sought to establish an oligarchy of the elite. They believed that they could manage foreign, fiscal, and war policies better than the existing government.The movement toward oligarchy was led by a number of prominent and wealthy Athenians, who held positions of power in the Athenian army at Samos in coordination with Alcibiades.