Bihu () is an important cultural festival unique to the Indian state of Assam"However, the festival to which utmost social importance is assigned by the people is Bihu, a festival that is neither pan-Indian in character nor observed with any religious fervour." and is of three types – '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"As folklorist Lila Gogoi (1988: 1) points out, Aryan, Austric, Mongolian, and Alpine elements are so closely intertwined in the Bihu festival that it is almost impossible to separate them analytically. Celebrated by almost all the communities of Assam, it is inspired by the seasonal changes and the commensurately changing agricultural cycles." —festivals which are uniquely Assamese are ones to which all communities of Assam had contributed elements."Bihu was born as a uniquely Axomiya festival, to which almost every community of Assam could claim to have lent some elements, but none could assert sole ownership." The Rongali Bihu is the most important of the three, celebrating spring festival. The Bhogali Bihu (or Magh Bihu) is a harvest festival, with community feasts. The Kongali Bihu (or Kati Bihu) is the sombre, thrifty one reflecting a season of short supplies and is an animistic festival.

The Rongali Bihu is the most important of them all, 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 Sino-Tibetan and Southeast Asia 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.

History Indigenous origin Etymology and regional traditions The word Bihu is believed to have been originally derived from the Deori (a Boro-Garo language) word Bisu which means "excessive joy".Gogoi, Dinesh(2015), Baapoti Hahun Bihu, Page 17-18, The word Bihu is probably a derived form of "Bisu" celebrated by the Deoris, which stands for "excessive joy"পৱন চন্দ্ৰ শইকীয়া, ‘কাতি বিহুৰ ৰূপৰেখা’, দেউৰী চুতীয়া, পৃষ্ঠাঃ ১০৯, "চুতীয়া ভাষাত বিহুক ‘বিচু’ বুলি কোৱ৷| হয় ৷ ‘বি’ মানে অতি আৰু ‘চু’ মানে আনন্দময় বুজায় । গতিকে ‘বিচু' শব্দই অতি আনন্দময় এটি উৎসৱক বুজায়। বিচু শব্দটি অপভ্ৰংশ হৈ ‘বিহু’ শব্দ উৎপত্তি হৈছে।" A Chutia folk explanation also associates Bisu with the cultivation of ahu rice. According to Mahanta (2018), ahu paddy, in ancient times, occupied an important place in Chutia agriculture, and cultivators guarding the crop from wild animals during the day and night passed the time through singing, dancing and other forms of merriment. The annual rejoicing associated with the luxuriant growth of the ahu crop came, in this tradition, to be known as Bisu.

The original form of Bihu continues among the Chutias, Sonowal Kacharis and Deoris. These groups, known as Sadiyal Kacharis, were associated with the historical Kingdom of Sadiya.Gogoi, Dinesh(2015), Baapoti Hahun Bihu, Page 17-18, The root of the Bihu festival lies with the earliest immigrants of Assams, the Kacharis. It is specially attributed to the Sadiyal Kacharis which includes Chutias, Sonowals, and Deoris. The other branches of Bodo-Kacharis, which include Boros, Dimasas, Rabhas, Tiwas, etc., have also been celebrating Bihu since ancient times. The Boros call it Baisagu, while the Dimasas, Tiwa and Rabha call it Bushu or Bushu Dima,"Busu Dima festival begins in Dima Hasao", Times Of IndiaPisu, Dumsi respectively.Gogoi, Dinesh(2015), Baapoti Hahun Bihu, Page 17-18, The root of the Bihu festival lies with the earliest immigrants of Assams, the Kacharis. It is specially attributed to the Sadiyal Kacharis which includes Chutias, Sonowals, and Deoris. The word Bihu is probably a derived form of "Bisu" celebrated by the Deoris, which stands for "excessive joy". Other festivals similar to it include the Baisagu of Bodos, Bushu of Dimasas, Pisu of Tiwas, and Dumsi of Rabhas. Noting its regional prevalence, Haliram Dhekial Phukan, a pioneering Assamese scholar, historian, and judicial officer in early colonial Assam, wrote,”Bihu Kamrupe nai, Saumare adhik”, meaning Bihu is not found in Kamrup; it is more prevalent in Upper Assam.হলিৰাম ঢেকিয়াল ফুকনৰ ৰচনাৱলী, p. 80

Early historical references The first reference of Bihu can be found in the copperplate inscription of the Chutia king Lakshminarayan. The inscription was found in Ghilamara region of Lakhimpur district in the year 1935 and it was issued in the year 1401 A.D. It states that the king Lakshminarayan had donated land grants to Brahmins to the west of Subansiri river on the auspicious occasion of Bihu.Neog, Maheswar, "Prachya Sasanavali", Introduction, p.189Barua, Swarnalata, "Chutia Jatir Buranji",p.40-41, "ফলিখনত স্বধয়াপুৰীশ্বৰ নন্দিশ্বৰৰ পুত্ৰ সত্যনাৰায়ণ আৰু এই সত্যনাৰায়ণৰ পুত্ৰ লক্ষ্মীনাৰায়ণ ৰজাই ৰবিদেৱ নামৰ এজন ব্ৰাহ্মণক বখনা গ্ৰামত ১৩২৩ শক (১৪০১ খ্ৰীঃ)ৰ বিষুব সংক্ৰান্তিৰ দিনা (অৰ্থাৎ ১ বহাগৰ বিহুৰ দিনা) ২০০ পুটি‌(পুৰা) ভূমি দান কৰাৰ কথা খোদিত আছে।" It reads, This means that on the pious occasion of Bihu, a Brahmin named Dvija Ravidev was granted land by the king. This indicates that Bihu played an important role in the social life of people of Assam at that period.

Yet another reference to Bihu can be found in the Deodhai Buranji which mentions that the capital of the Chutia kingdom, Sadiya, was suddenly attacked by the Ahom forces on the first day of Bihu/Bisu in 1524 (first Wednesday of Bohag/Vaisakha), when the people were busy celebrating Bihu. The Ahom general Phrasenmung Borgohain, upon the advice of a Chutia general (who sided with the enemies), played the Bihu Dhul (on Ujha Bisu day, i.e. 7th Bohag/Vaisakha) to trick the Chutias, which ultimately led to their defeat.

Religious traditions and myths According to a tradition recorded in the Deo Buranji, Kechai-khati or Kolimoti, the goddess associated with Sadiya, the capital of the Chutia kingdom, was regarded as the originator of Bihu. Late historian Hem Buragohain states that the bloodthirsty Kolimoti—described in the tradition as Shiva's sister—was believed to have initiated Bihu. In Deori religious tradition, Gira-Girasi, also called Burha-Burhi, are regarded as the senior ancestral deities; Baliya Baba (Pisa Dema) and Kechai-khati (Pisasi Dema) are described as their son and daughter respectively.

In local folklore, it is said that Bordoisila (Bardai Sikhla in Bodo) (meaning north-westerly winds in Assamese) was the daughter of God Earth who married a bridegroom of some distant land. Bordoisila visits her mother's home once a year during springtime, which indicates the beginning of Bihu and leaves after a few days, which indicates the end of Bihu. Assam experience strong gale (wind) at that period, which marks the beginning of Bihu and another strong gale after her departure, which is devastating. The word Bordoisila is derived from the Bodo word Bordaisikhla, which means "girl of storm" (Sikhla meaning girl and Bardai meaning storm). There is even a dance with the same name performed among Boro people during Baisagu, which points to the origin of Bihu in the Bodo-Kachari groups."BOHAG BIHU",Outlook India

Chotor and Bohag Bihu cycle

As per traditions, Bohag Bihu celebrations formerly began during the month of Chot. The period preceding the principal Bohag festivities was known as Rati Bihu or Chotor Bihu, during which young men and women performed at night beneath large trees and at sacred places like the grounds of the Than (temple). It is believed that Bihu was brought down at night from the Tameswari shrine to a large tree, where young men and women perform beneath mango or aahat trees. Chot Bihu is also associated with the youthful aspect of the goddess Kolimati; the flowering of the tarua kadam is regarded as a sign of her attaining youth and heralding the beginning of the festival. Local Chutia forms of Chotor Rati Bihu are still recorded in places such as Barhola and Basa Daiyang in the Jorhat-Golaghat region, where young men and women traditionally perform at night beneath large mango or aahat trees. The repertoire includes jura naam and songs of love and separation, while competitions between pepa players are also recorded. A comparable Rati Bisu tradition is also preserved among the Deoris. The Deoris are recorded as celebrating a "night Bisu", with young people gathering during Phagun and Chaitra for communal Bisu rehearsals; during Bohagiyo Bisu, singing and dancing also continue through the night.

The last day of Chaitra or the first Tuesday of Bohag was when the Rati Bihu ended. This was known as the Uruka (derived from the Deori-Chutia Urukuwa meaning to end). The temple dancers Deodhani danced the entire night and were believed to be possessed by the goddess Kechai-khati (kolimoti), signalling that she had descended upon earth from heaven (Bihu nomai ona). This belief of the goddess arriving during the Bihu season each year can still be found in Bihu songs as,

The day after Uruka, i.e. the first Wednesday, was celebrated as Goru Bihu. This tradition of cattle rites is the same as that followed by the Boros in Bwisagu, indicating the common roots of both the festivals. During the night of Goru Bihu, people danced Bihu in separate groups in the Thans where animal sacrifice took place. After the sacrifices to the goddess, the young folk visited the households of the village, which was the start of . This old tradition of starting from the temple is still followed by the Deoris, some Sonowals, Chutias and Morans as well as the people of Sadiya. In other communities, the temple has been replaced by the Namghar.

Some old Assamese Bihu folklore still hints at this tradition:

The festivities of Bohag Bihu continued for a week and ended with the rite by which the goddess was bid farewell. In this rite, a boat was first prepared out of a banana stem and decorated with flowers and offerings. Then, it was carried to the banks of the river where a duck/chicken was put inside the boat and allowed to float as a symbol of sacrifice. After performing the rite, the people returned to their homes, singing along the way with the beats of the Dhul and the tunes of the Pepa.

This tradition of floating the boat can be heard in Bihu songs as:

Hurai Rangali and Husori Tradition