Athenian democracy developed in the Greek city-state of Athens, comprising the central city-state of Athens and the surrounding territory of Attica, around 500 BC. Athens was one of the very first known democracies and probably the most important in ancient times. Other Greek cities set up democracies, most but not all following an Athenian model, but none were as powerful or as stable (or as well-documented) as that of Athens. It remains a unique and intriguing experiment in direct democracy where the people do not elect representatives to vote on their behalf but vote on legislation and executive bills in their own right. Participation was by no means open to all inhabitants of Attica, but the in-group of participants was constituted with no reference to economic class and they participated on a scale that was truly phenomenal.

Solon (594 BC), Cleisthenes (509 BC), and Ephialtes of Athens (462 BC) all contributed to the development of Athenian democracy. Historians differ on which of them was responsible for which institutions, and which of them most represented a truly democratic movement. It is most usual to date Athenian democracy from Cleisthenes, since Solon's constitution fell and was replaced by the tyranny of Peisistratus, whereas Ephialtes revised Cleisthenes' constitution relatively peacefully. Hipparchus, the brother of the tyrant Hippias, was killed by Harmodius and Aristogeiton, who were subsequently honored by the Athenians for their alleged restoration of Athenian freedom.

The greatest and longest-lasting democratic leader was Pericles; after his death, Athenian democracy was twice briefly interrupted by oligarchic revolution towards the end of the Peloponnesian War. It was modified somewhat after it was restored under Eucleides; the most detailed accounts are of this fourth-century modification rather than the Periclean system. It was suppressed by the Macedonians in 322 BC. The Athenian institutions were later revived, but the extent to which they were a real democracy is debatable.