Festivals were the chief expressions of religious life and practice in Hellenic cities in classical times. There is a wealth of information about Athenian festivals in particular, thanks to frequent reference to them in inscriptions and in ancient writers.

The way the annual calendar was articulated corresponded in large measure to the sequence of festivals, and is known with certainty for Attica. It was originally Solon who shaped the Attic calendar. When the constitution was overthrown by an oligarchic regime in 410 B.C., the People's Assembly appointed Nicomachus to draw up a concise calendar and make public the calendar of sacrifices. We still have some fragments of the inscription with Nicomachus' text, which was set up in the King's Stoa in the Agora.

The Attic year began with the month Hekatombaion (July), after the end of the cereal harvest. The other eleven months were then as follows: Metageitnion, Boedromion, Pyanepsion, Maimakterion, Poseideon, Gamelion, Anthesterion, Elaphebolion, Mounichion, Thargelion, and Skirophorion. They were named for their festivals: to take two examples, in Hekatombaion there was a hecatomb festival in honour of Apollo, and in Mounichion there was the festival of Artemis at Mounichia. Some major festivals - for instance the Panathenaea (in Hekatombaion) or the Thesmophoria (in Pyanepsion) or the Great Dionysia (in Elaphebolion) were not reflected in the name of the month in which they occurred.

In Attica the content of the festivals was markedly heterogeneous. Some (such as the Maimakteria or the Anthesteria) had to do with the changing seasons; some with the farming year (seedtime, harvest, vintage), or with the beginning and end of the calendar year; and some with phratria activities (the Apaturia) or with exclusively female cult celebrations.

At Athens it was the archon basileus, the Eponymous Archon and the priests who were competent to organize the city festivals, and responsible for them. (Traditional festivals in the demes of Attica were something of an exception: they were organized by the demes themselves). The great organized festivals - such as the Panathenaea or the Dionysia - afforded an opportunity for a show of strength, since the allied cities took part, often without the option, in them. As Athenian hegemony disintegrated in the fourth century, these celebrations lost their former lustre.