The Ecclesia was the Assembly of Athenian Citizens. From 451 B.C. every adult Athenian citizen who had full civil rights (that is those whose parents were both citizens and those who had completed their two-year military service) had the right to participate in it. Women, metics (resident foreigners) and slaves, who did not enjoy civil rights, were not eligible; neither were those who had committed offences (atimoi). Citizens who were sent on expeditions, and residents of the countryside could not in practice participate in every meeting for practical reasons. (Thucydides Historyof the Peloponnesian War 8.72). The most distant point in Attica was forty-five kilometres away, and for this reason, most voters participated in the meetings only when serious or complex problems arose. After the restoration of democracy in 404/3 B.C. a fee was introduced for the citizens who took part in Assembly meetings, known as the Assembly fee.

The Assembly of Citizens in which all power originated, was the main instrument of Athenian democracy. It discussed important issues related to the constitution, passed laws and elected military leaders and financial office holders (Aristotle, Athenian Constitution 43. 1-2 and 44.4). In addition, it decided on the number of citizens, metics and slaves that needed to be mobilised; had the authority to confiscate property; impose exile and even the death penalty. Furthermore, it determined Athenian foreign policy, deciding on such matters as whether to make peace or wage war. It made alliances with other cities and states, receiving foreign ambassadors and electing their own.