Akitu or Akitum (Sumerian: 𒀉𒆠𒋾, romanized: a-ki-ti) (Akkadian: 𒀉𒆠𒌈, romanized: akītu(m)) is a spring festival and New Year's celebration, held on the first day of the Assyrian and Babylonian Nisan in ancient Mesopotamia and in Assyrian communities around the world, to celebrate the sowing of barley. Akitu originates from the Sumerian spring New Year festival of Zagmuk.

The Babylonian festival traditionally started on 4 Nissan, the first month of the year, as a celebration of the sowing of barley. All the people in the city would celebrate, including the awilu (upper class), muskena (middle class), wardu (lower class), High Priest, and the King.

The priest of Ésagila (Marduk's house) would recite sad prayers with the other priests and the people would answer with equally sad prayers which expressed humanity's fear of the unknown. This fear of the unknown explains why the high priest would head to the Ésagila every day asking for Marduk's forgiveness, begging him to protect Babylon, his holy city, and asking him to have favor on the city. This prayer was called "The Secret Of Ésagila". It reads:

"Lord without peer in thy wrath,
Lord, gracious king, lord of the lands,
Who made salvation for the great gods,
Lord, who throwest down the strong by his glance,
Lord of kings, light of men, who dost apportion destinies,
O Lord, Babylon is thy seat, Borsippa thy crown
The wide heavens are thy body....
Within thine arms thou takest the strong....
Within thy glance thou grantest them grace,
Makest them see light so that they proclaim thy power.
Lord of the lands, light of the Igigi, who pronouncest blessings;
Who would not proclaim thy, yea, thy power?
Would not speak of thy majesty, praise thy dominion?
Lord of the lands, who livest in Eudul, who takest the fallen by the hand;
Have pity upon thy city, Babylon
Turn thy face towards Esagila, thy temple
Give freedom to them that dwell in Babylon, thy wards!"

On the second day the high priest would bathe in the Euphrates River before performing special prayers at the temple with the other priests.

On the third day special craftsmen would create two puppets made of wood, gold, and precious stones and dress them in red. These puppets were set aside and would be used on the sixth day. Meanwhile, the priests and the people would pray before sunset. The king took a statue of Nabu son of Marduk into the temple to be worshipped.

The fourth day involved memorials and celebration. The priests would tell creation stories while the people would sing and dance.

On this day the public would gather at the river to eat together and celebrate. Meanwhile, the king was brought to the temple, where he would show humility before the gods. The high priest would slap the king as a way to further induce humility; the king's tears were seen as a good omen for the coming year. The priests would then reintroduce the king to the public.