• Anthesteria (in early spring),
• the Greater or City Dionysia (in late spring)
• Lesser or Rural Dionysia (in mid-Winter [Dec-Jan]),
• Lenaea (in winter).

The Athenian year  consisted of twelve months, with the first month, Hecatombaion, beginning around midsummer at the new moon before the summer solstice. (Parke, 29)   From the music, singing, and dancing at the festivals of Dionysus developed the dithyramb [choral lyric with exchanges between the leader and the chorus] and ultimately Greek drama.

Anthesteria: Festival of the Vine Flower

In Athens, as in other Ionic cities, there was a custom each spring to celebrate the "Festival of the Vine Flower" This is  a feast of the dead as well.

(Anthesteria), parts of which were sacred to Dionysus as Lord of the Vine.
Day 1: Pithoigia ("Opening of the Wine-Jars") the jars of new wine were opened. Then master and slave partook of the wine, side by side.
Day 2: Choes ("Pitchers") The second day was known as "Beakers", on which they blessed the new wine and competed in drinking from it to the sound of trumpets. On that day, children had a holiday from school and were supplied with small beakers in order to participate in the festivities.

 The festival began with a drinking contest, where the men in silence, at a separate tables consumed wine. The slaves were allowed to participate in this contest as equals. Athenians considered Choës a day of defilement: citizens painted house doors with pitch and chewed buckthorn leaves while ancestral spirits, the Keres, were though to have filled the city.

Swinging like Erigone: During the day, the virgin Athenian girls let the boys push them in swings, associating themselves with the tragic figure of Erigone. Erigone's swinging memorialized the sacred love-death of the tragic Erigone who hung herself after discovering her father dead in a well.
Her father was Ikarios, the first man Dionysos showed how to make wine and whose death came at the hands of the ungrateful villagers he had first shared the nectar with as they believed he had poisoned them. Before Erigone's death she marries Dionysus and the girls would sing a song where they would touch the grape at the height of their ascent.  The Roman poet Ovid has her become the god's wife by eating a grape, but in Aristotle's time a song of Erigone was penned by a famous erotic poet. Kerényi notes this rite that has roots as far back as ancient Crete and Sumer, judging by unearthed statuettes of swinging girls. Erigone's swinging symbolizes the moment of death and love, a theme rarely explored by artists in the present.

This playful ritual formed a prelude for another sacred marriage, that of the Athenian queen with Dionysos.

 Day 3: Chytroi ("Cooking-Pots") Pots containing cooked vegetables and seeds (traditional food for the dead) were left out for the wandering spirits. However, precautions were taken to prevent the spirits from coming too close: people chewed hawthorn, smeared their doors with pitch, and tied ropes around the temples. At the end of the festival, they drove out the spirits, saying, "Out you Keres, it is no longer Anthesteria!"

SACRED MARRIAGE or hieros gamos: It was probably on this day--actually on the evening of the day preceding, since for the Greeks the new day began at sunset--that the sacred marriage or hieros gamos was celebrated the sacred marriage of a mortal woman to the god.

A public procession (pompe) set forth, in which Dionysus' image was paraded through the streets of Athens in a ship driven on wheels. Accompanying it, were bands of participants dressed as satyrs and maenads.
On reaching the Temple of 'Dionysus in the Bog' - some distance outside the walls - there took place the ritual marriage of the Queen to Dionysus.

Dionysos was formally wedded to the Basilinna, wife of the Archon Basileus (King Archon). The bride was escorted from the sanctuary of Dionysos in the Marshes to a building called the Boukoleion ("ox-herd building") in or near the Agora. Before the ceremony fourteen noble women called Gerarai ("ladies of honor") made offerings at fourteen altars in the sanctuary. 

The union of queen and god took place just after sunset at the end of Choës in the Boukolion, a small house in the Agora, "the bull's stable," which was the ancient official residence of the king. A reference to bull's role as a sacred amimal for many millennia.

The wedding, a fertility rite, is explained by the myth that in earlier times the Athenian hero Theseus gave up his bride, the Cretan princess Ariadne, to Dionysos.

To be Queen would be a great honor and the only woman in the room when the rites were administered. Perhaps the wife of a civic magistrate given the title of 'the King Magistrate', who was, among other things, supervisor of religious affairs or another chosen for mysterious reasons. The groom might be a priest of Dionysos or the Archon Basileus, dressed and masked as Dionysos.  

Greater Dionysia was celebrated in Athens in the late spring for five days.  Pisistratus, in the second half of the sixth century B.C., introduced the cult of Dionysos in the city as an addition to the popular rural one.

Dionysian theatre was noted for its democratic nature for everyone was invited to be entertained. During the celebration business life stopped, prisoners were freed in order to participate.

In the city, this festival opened with a phallic parade, in which the god's image was born through the streets of Athens from outside the walls and brought to the Temple of Dionysus on the slopes of the Acropolis. After completion of the sacrifices, the image was now born to the theatre dancing floor (the orchestra) accompanied by torch bearers - and there it stood throughout the presentation of the plays over the next several days but not before the komos, or revel, a night-long feast and celebration.

AGRIONIA, an ancient Greek festival, which was celebrated annually at Orchomenus in Boeotia and elsewhere, in honour of Dionysus Agrionius, by women and priests at night. The women, after playfully pretending for some time to search for the god, desisted, saying that he had hidden himself among the Muses.

The tradition is that the daughters of Minyas, king of Orchomenus, having despised the rites of the god, were seized with frenzy and ate the flesh of one of their children. At this festival it was originally the custom for the priest of the god to pursue a woman of the Minyan family with a drawn sword and kill her. (Plutarch, Quaest. Rom. 102, Quaest. Graecae 38.)
1911 Encyclopedia -- Volume 1 Index

Rural or Lesser Dionysia
The Rural Dionysia would see repeat performances of the plays in areas outside of Athens. The Greeks loved their dramas - and people would travel from all over to witness these competitions. They lasted for almost six days, and included processions, songs, dances, and feasts.

 During the Hellenistic Age, after Alexander had brought Greek culture to the places he conquered, no city was complete without its Greek theater. Special seats of honor were reserved for Priests of Dionysos.

This festival took place during the month Poseideon (December), at various times in the various demes (villages) of Attica, the countryside around Athens. A feature of the celebration was a procession in which a large model of a phallos (a male organ) was carried along, accompanied by a noble lady serving as Basket-Bearer with a basket of raisins or other fruit. A billy-goat was led along to be sacrificed to Dionysos.

On  the second day of the festival, there is the Askôliasmos, a contest to see who can balance longest on top of a greased, inflated wine-skin (askos). One-legged games such as standing on one leg, one-legged races, one-legged tag with the raised leg, one-legged hopping endurance were also enjoyed.

These traditions were the foundation the Romans built the more elaborate and widely celebrated Saturnalia upon.
 

Lenaea (in winter)

 Lenaea was the festival were the wine of the season was born. The theater was an integral part of Dionysus’s festival Lenaea. Many of the great Greek tragedies actually originated during this festival. Lenaea took place in the beginning of winter, the followers of Dionysus referred to the time the wine finished fermenting as its birth. They also believed this coincided with one of the births of Dionysus (Kerenyi 284).

Aristophanes' comedy the Acharnians, presented in 425 BCE at the Lenaia, features a chorus from the deme of Acharnai, who have been displaced from their village by Spartan invasions of Attica and forced inside the walls of Athens. The hero, Dikaiopolis ("just city"), makes a private peace with the Spartans. (The treaty is a skin full of wine, since the word for "libations" also meant "treaty.") He then conducts his own private celebration of two Dionysiac festivals, the Rural Dionysia and the Choes.