Vesak (Pali: Vesākha; Sanskrit: Vaiśākha), also known as Buddha Jayanti, Buddha Purnima and Buddha Day, is a holiday traditionally observed by Buddhists in South Asia and Southeast Asia as well as Tibet and Mongolia. It is the most important Buddhist festival. The festival commemorates the birth, enlightenment (Nibbāna), and death (Parinirvāna) of Gautama Buddha in Theravada, Tibetan Buddhism and Navayana.

The name Vesak is derived from the Pali term vesākha or Sanskrit vaiśākha for the lunar month of Vaisakha, which is considered the month of Buddha's birth. In Mahayana Buddhist traditions, the holiday is known by its Sanskrit name (Vaiśākha) and derived variants of it.

In the East Asian tradition, a celebration of Buddha's Birthday typically occurs around the traditional timing of Vesak, while the Buddha's awakening and passing away are celebrated as separate holidays that occur at other times in the calendar as Bodhi Day and Nibbāna Day. In the South Asian tradition, where Vesak is celebrated on the full moon day of the Vaisakha month, the Vesak day marks the birth, enlightenment, and the ultimate passing away of the Buddha.