The ecclesia or ekklesia () was the principal assembly of the democracy of ancient Athens during its Golden Age (480–404 BCE). It was the popular assembly, opened to all male citizens over the age of 30 by Solon in 594 BC meaning that all classes of citizens in Athens were able to participate, even the thetes. The ecclesia opened the doors for all citizens, regardless of class, to nominate and vote for magistrates - indirectly voting for the Areopagus - have the final decision on legislation, war and peace, and have the right to call magistrates to account after their year of office. In the 5th century BC their numbers amounted to about 43,000 people. However, only those wealthy enough to spend much of their time away from home would have been able to participate until Pericles' reforms in early 451-2 BCE allowing payment for jurors. The assembly was responsible for declaring war, military strategy, and electing strategoi and other officials. It originally met once every month, but later it met three or four times per month. The agenda for the ecclesia was established by the Boule, the popular council. Votes were taken by a show of hands.

A quorum of 6,000 was required sometimes to do business. The ecclesia elected by lot annually the Boule or council. Some of their power under Solon was delegated to the Courts by Pericles in his reforms.

A gang of slaves, called Scythians, carrying ropes dipped in red ochre (miltos, hence Miltiades, i.e. the Red-Haired) would travel through the city on the days the Ecclesia was to meet, and use their ropes to lash those citizens not in attendance. With garments thus stained, shamed citizens could legally carry out no business until they visited the meeting grounds of the Ecclesia on the hill called the Pnyx.