Magha Puja (also written as Makha Bucha Day) is the third most important Buddhist festival, celebrated on the full moon day of the third lunar month in Cambodia, Laos, Thailand, Sri Lanka and on the full moon day of Tabaung in Myanmar. It celebrates a gathering that was held between the Buddha and 1,250 of his first disciples, which, according to tradition, preceded the custom of periodic recitation of discipline by monks.

On the day, Buddhists celebrate the creation of an ideal and exemplary community, which is why it is sometimes called Saṅgha Day, the Saṅgha referring to the Buddhist community, and for some Buddhist schools this is specifically the monastic community. In Thailand, the Pāli term Māgha-pūraṇamī is also used for the celebration, meaning 'to honor on the full moon of the third lunar month'.

Finally, some authors referred to the day as the Buddhist All Saints Day. 

In pre-modern times, Magha Puja has been celebrated by some Southeast Asian communities. But it became widely popular in the modern period, when it was instituted in Thailand by King Rama IV in the mid-19th century. From Thailand, it spread to other South and Southeast Asian countries. Presently, it is a public holiday in some of these countries.

It is an occasion when Buddhists go to the temple to perform merit-making activities, such as alms giving, meditation and listening to teachings. It has been proposed in Thailand as a more spiritual alternative to the celebration of Valentine's Day.