"Loy Krathong" (Thai: ลอยกระทง) is a Siamese festival celebrated annually throughout the Kingdom of Thailand and in nearby countries with significant South Western Tai cultures (Laos, Shan, Mon, Tanintharyi, Kelantan, Kedah and Xishuangbanna). The name could be translated as "to float ritual vessel or lamp," and comes from the tradition of making krathong or buoyant, decorated baskets, which are then floated on a river. Many Thais use the krathong to thank the Goddess of Water, the Hindu Goddess Ganga (river in Northern India), Phra Mae Khongkha (Thai: พระแม่คงคา). This festival can see the traces of its origin back to India.

Loy Krathong takes place on the evening of the full moon of the 12th month in the traditional Thai lunar calendar, thus the exact date of the festival changes every year. In the Western calendar this usually falls in the month of November. In Chiang Mai, the festival lasts three days, and in 2018, the dates were 21–23 November.

In Thailand, the festival is known as Loi Krathong. Outside Thailand, this festival is celebrated under different names, including Myanmar as the "Tazaungdaing festival", Sri Lanka as "Il Full Moon Poya", and China as "Lantern Festival".