The Baro-Bhuyans (or Baro-Bhuyan Raj; also Baro-Bhuians and Baro-Bhuiyans) were confederacies of soldier-landowners in Assam and Bengal in the late Middle Ages and the early modern period. The confederacies consisted of loosely independent entities, each led by a warrior chief or a landlord. The tradition of Baro-Bhuyan is peculiar to both Assam and Bengal and differ from the tradition of Bhuihar of Uttar Pradesh and Bihar—in Assam this phenomenon came into prominence in the 13th century when they resisted the invasion of Ghiyasuddin Iwaj Shah and in Bengal when they resisted Mughal rule in the 16th century.

Baro denotes the number twelve, but in general there were more than twelve chiefs or landlords, and the word baro meant many. Thus, Bhuyan-raj denoted individual Bhuyanship, whereas Baro-Bhuyan denoted temporary confederacies that they formed. In times of aggression by external powers, they generally cooperated in defending and expelling the aggressor. In times of peace, they maintained their respective sovereignty. In the presence of a strong king, they offered their allegiance. In general each of them were in control of a group of villages, called cakala, and the more powerful among them called themselves raja. The rulers of the Bhuyanships belonged to different ethnic, religious or social backgrounds.

In 13th century Brahmaputra Valley the system of Baro-Bhuyan Raj (confederacy) was formed from the petty chieftains—the remaining fragments of the erstwhile Kamarupa state. They often resisted foreign invasions (Ghiyasuddin Iwaj Shah in the 13th century), removed foreign rule (Hussain Shah in the 16th century) and sometimes usurped state power (Arimatta in the 14th century). They occupied the region west of the Kachari kingdom in the south bank of the Brahmaputra river, and west of the Chutiya kingdom in the north bank. These included areas of Nagaon, Darrang and Sonitpur districts. Subsequently, the Baro Bhuyan rule ended in the 16th century as they were squeezed between the Kachari kingdom and the Kamata kingdom in the west and were slowly overpowered by the expanding Ahom kingdom in the east.

In Bengal, the most prominent Baro-Bhuyan confederacy was led by Isa Khan of Sonargaon in the 16th century, which emerged during the disintegration of the Bengal Sultanate in the region, as a resistance to the Mughal expansion. They carved the land of Bhati and other areas of Bengal into twelve administrative units or Dwadas Bangla. The Baro-Bhuyans gradually succumbed to the Mughal dominance and eventually lost control during the reign of emperor Jahangir, under the leadership of Islam Khan I, the governor of Bengal Subah.

Epigraphic sources indicate that the Kamarupa state had entered a state of fragmentation in the 9th century when the tradition of granting away police, revenue and administrative rights to the donee of lands became common. This led to the creation of a class of landed intermediary between the king and his subjects—the members of which held central administrative offices, maintained economic and administrative links with in their own domain and propagated Indo-Aryan culture. This gave rise to the condition that individual domains were self-administered, economically self-sufficient and capable of surviving the fragmentation of central authority, when the Kamarupa kingdom finally collapsed in the 12th century.

Amalendu Guha claims that the Baro-Bhuyan emerged in the 13th century from the fragmented remains of the Kamarupa chieftains. Nevertheless, not all local Kamarupa administrators (samanta) became Bhuyans and many were later-day migrant adventurers from North India. Though there exists many legendary accounts of the origin of the Baro Bhuyan these accounts are often vague and contradictory.

This original group is often referred to as the Adi Bhuyan, or the progenitor Bhuyans. The Adi-charita written in the late 17th century is the only manuscript which mentions the Adi-Bhuyan group. However, Maheswar Neog has called the account as spurious or fabricated.

Nevertheless, their presence is recorded in the Ahom Buranjis, where it is recorded that they were instrumental in ending the rule of the Kachari kingdom. As a reward, the Ahom king Suhungmung (1497–1539) settled these Bhuyans (originally living in Rowta-Temoni, present-day Darrang and Nagaon) in Kalabari, Gohpur, Kalangpur and Narayanpur as tributary feudal lords. Over time, these Bhuyans grew very powerful but they were later subjugated by the Ahom king Jayadhwaj Singha. The Saru Baro Bhuyan is a branch of the Bar Baro Bhuyan that split and went west.