The Plague of Athens is an epidemic that devastates the city-state of Athens in ancient Greece during the second year of the Peloponnesian War (430 BCE) when an Athenian victory still seems within reach.

The plague kills an estimated seventy-five thousand to one hundred thousand people and is believed to have entered Athens through Piraeus, the city's port and sole source of food and supplies.

Much of the eastern Mediterranean also sees an outbreak of the disease, albeit with less impact.

The plague has serious effects on Athens' society, resulting in a lack of adherence to laws and religious belief; in response, laws become stricter, resulting in the punishment of non-citizens claiming to be Athenian.

The plague returns twice more, in 429 BEC and in the winter of 427/426 BC.

Some thirty pathogens have been suggested as causing the plague.

Modern historians will disagree on whether the plague was a critical factor in Athens’ loss of the war.

However, it is generally agreed that the loss of this war may have paved the way for the success of the Macedonians and, ultimately, the Romans.