Kathina is a Buddhist festival which comes at the end of Vassa, the three-month rainy season retreat for Theravada Buddhists in Bangladesh, Cambodia, Laos, Malaysia, Myanmar, Singapore, Sri Lanka, India, Thailand, and Vietnam. The season during which a monastery may hold Kathina is one month long, beginning after the full moon of the eleventh month in the Lunar calendar.

Vassa is the three-month annual retreat observed by Theravada Buddhists. Taking place during the wet season, Vassa lasts for three lunar months, usually from July to October.