Krishna Janmashtami marks the birth of Krishna, the eighth incarnation of Vishnu, on the eighth day (ashtami) of the dark fortnight of Bhadrapada (August–September), at midnight. King Kamsa, having heard a prophecy that the eighth child of his sister Devaki would kill him, imprisoned Devaki and her husband Vasudeva and killed each of their first seven children. When the eighth — Krishna — was born at midnight, the prison doors opened of their own accord, the guards fell into deep sleep, and Vasudeva carried the newborn across the river Yamuna to Gokul, where he was exchanged with the newborn daughter of Yashoda. Krishna grew up among cowherds in Vrindavan, unknown to Kamsa.

The night of Krishna's birth, by classical reckoning, was a stormy one — the Yamuna in flood, the rain heavy, the serpent Shesha hovering over Vasudeva with hood spread to shield the child. Devotional reading: every devotee's chest at midnight on Janmashtami is the prison cell from which Krishna is born again.

Devotees keep a partial or complete fast through the day, breaking it only after the midnight puja. Temples are decorated; the idol of the infant Krishna (Laddu Gopal) is bathed, dressed, and rocked in a small cradle. Bhajans are sung through the evening, building to the moment of birth — exactly midnight.

In Maharashtra and other parts of western India, Dahi Handi follows the next day: a clay pot of curd is hung high above the street, and young men form human pyramids to break it open — a play-re-enactment of Krishna stealing butter and curd from the gopis of Vrindavan.