Bhisma Dwadashi is observed in the sacred memory of one of the most loved characters of Mahabharata, Pitamah Bhisma, who fell in the great battle of the Kurukshetra.

Bhisma, the son of King Santanu and Ganga, had the boon of self willed death or Ichcha Mrityu, and after being bombarded with arrows by Arjuna; lay on a bed of arrow waiting for fifty eight days and an auspicious day to leave his mortal body behind and give up his soul to the Gods. He chose the day when the Uttarayana or the northward journey of the Sun started to leave his body behind.

Bhisma Dwadashi is observed on the twelfth day in the month of Magha or January-February during the shukla paksha according to the Hindu calendar. This day is also known as Magha Shukla Dwadashi. According to the epic Mahabharata, the Pandavas performed the last rites of the erudite BHisma on this day in the bank of the Ganga.

Bhisma Dwadashi is the second most auspicious day amidst the Bhishma Panchaka Vrat, which is observed from the Bhishma Ekadashi till the Maghi Purnima.  It is an auspicious day which is observed by the Vaishnavas (that is the followers of Vishnu), as well as the Shaivites (that is the devotees of Lord Shiv)a.

As the last rites of Bhisma was performed by the Pandavas on this day, it is generally considered to be an auspicious day; and according to popular beliefs, offering Tarpana and doing the last rites or Shradh for the ancestors   on this day is highly beneficial. Some people also offer tarpan, or water in the name of Bhisma as he was childless.

The Bhisma Dwadashi is celebrated amidst great fanfare in ISKCON temples, the Vrindavana Krishna Temples, Banke Bihariji Temple and in the Lord Jagannath Temple in Puri.