Bihu is a set of three important cultural festivals unique to the Indian state of Assam – ‘Rongali’ or ‘Bohag Bihu’ observed in April, ‘Kongali’ or ‘Kati Bihu’ observed in October or November, and ‘Bhogali’ or ‘Magh Bihu’ observed in January. The festivals present an admixture of Tibeto-Burman, Austroasiatic and Indo-Aryan traditions entwined so intricately that it is impossible to separate them festivals which are uniquely Assamese to which all communities of Assam had contributed elements. The Rongali Bihu is the most important of the three, celebrating spring festival. The Bhogali Bihu or the Magh Bihu is a harvest festival, with community feasts. The Kongali Bihu or the Kati Bihu is the sombre, thrifty one reflecting a season of short supplies and is an animistic festival.

The Rongali Bihu coincides with the Assamese New Year and as well as with other regions of Indian subcontinent, East Asia and South-East Asia, which follow the Hindu calendar and Buddhist calendar. The other two Bihu festivals every year are unique to Assamese people. Like some other Indian festivals, Bihu is associated with agriculture, and rice in particular. Bohag Bihu is a sowing festival, Kati Bihu is associated with crop protection and worship of plants and crops and is an animistic form of the festival, while Bhogali Bihu is a harvest festival. Assamese celebrate the Rongali Bihu with feasts, music and dancing. Some hang brass, copper or silver pots on poles in front of their house, while children wear flower garlands then greet the new year as they pass through the rural streets.

The three Bihu are Assamese festivals elders in family, fertility and mother goddess, but the celebrations and rituals reflect influences from Southeast Asia and Sino-Tibetan cultures. In contemporary times, the Bihus are celebrated by all Assamese people irrespective of religion, caste or creed. It is also celebrated overseas by the Assamese diaspora community living worldwide.

The term Bihu is also used to imply Bihu dance otherwise called Bihu Naas and Bihu folk songs also called Bihu Geet.