Obon (お盆; [o.boꜜɴ]) or just Bon (盆; [boꜜɴ]) is a fusion of the ancient Japanese belief in ancestral spirits and a Japanese Buddhist custom to honor the spirits of one's ancestors. This syncretic folk Buddhist custom has evolved into a family reunion holiday during which people return to ancestral family places and visit and clean their ancestors' graves when the spirits of ancestors are supposed to revisit the household altars. It has been celebrated in Japan for more than 500 years and traditionally includes a dance, known as Bon Odori.

The festival of Obon lasts for three days; however, its starting date varies within different regions of Japan. When the lunar calendar was changed to the Gregorian calendar at the beginning of the Meiji era, the localities in Japan responded differently, which resulted in three different times of Obon. Traditionally, Obon was celebrated on the 15th day of the seventh month of the lunar calendar.

Obon is now observed during one of the following periods:

These days are not listed as public holidays, but it is customary for people to be given leave.

Within the Japanese diaspora, the obon is usually tied to a fundraising event for a temple, church, and even non-sectarian Japanese community organizations. As a result, Japanese organizations within a particular region will often coordinate their dates on different weekends throughout the summer as the participants were not expected to be given leave during the workweek if the date fell on a weekday, and to allow for the greater community to support each other's events. It isn't uncommon for families in regions with a larger Japanese emigrant population to visit multiple festivals in support of the greater community.

The Japanese Obon Festival is heavily influenced by the Ghost Festival of Buddhism and the Chinese Taoist Zhongyuan (中元) Festival.

Before Buddhism came to Japan, there was already a custom in place to beckon the deceased home to their families twice a year, both in spring and autumn, on the night of the full moon. This custom already had a close connection to the ancestor-veneration characteristic it has in modernity.

The Buddhist tradition originates from the story of Maha Maudgalyayana (Mokuren), a disciple of the Buddha, who used his supernatural powers to look upon his deceased mother only to discover she had fallen into the Realm of Hungry Ghosts and was suffering. Greatly disturbed, he went to the Buddha and asked how he could release his mother from this realm. Buddha instructed him to make offerings to the many Buddhist monks who had just completed their summer retreat on the fifteenth day of the seventh month. Mokuren did this and, thus, saw his mother's release. He also began to see the true nature of her past selflessness and the sacrifices she had made for him during her lifetime. The disciple, happy because of his mother's release from suffering and grateful for her many kindnesses, danced with joy. From this dance of joy comes the Bon Odori or "Bon Dance", a time during which ancestors and their sacrifices are remembered and appreciated. See also: Ullambana Sutra.