Festivals were a very important part of life in ancient Mesopotamia. There would have been many throughout the year and they varied from city to city. The most important festivals would have been connected with agricultural and pastoral activities such as sheep-shearing. Some took place on specific dates, others were related to myths or celebrated local gods and goddesses. A number of important festivals required the presence and participation of the king. The king was viewed as the gods' representative on earth (see Kingship) and played a central religious role.

For the Babylonians, the twelve days of the New Year ceremonies, celebrated in the springtime, were the most important annual festival. They included a procession of the statue of the god Marduk through the streets to a temple outside the city walls. When the king arrived he was slapped across the face by the high priest to show he was less important than the god and his symbols of office were removed. After spending some time in the main temple, the king's face was again slapped (tears coming to his eyes was viewed as a good sign) and his regalia returned to him. He could thus rule for the next year having been reappointed by the god. During the festival the Epic of Creation was read (or perhaps acted) out (see Myths).

Similar festivals took place in other cities with the divine images being carried in procession. This displayed the temple's wealth and pomp.

Many surviving hymns and prayers may be connected with festivals. An example is the agushya hymn. This describes how the god Ea had instigated a festival commemorating the warrior goddess Ishtar in which people danced madly about the streets.