The Ahom (Pron: /ˈɑːhɒm/) or Tai Ahom (Ahom: 𑜄𑜩 𑜒𑜑𑜪𑜨; Assamese: টাই-আহোম) are an ethnic group primarily found in the Indian states of Assam and Arunachal Pradesh. They are the admixed descendants of Tai peoples who migrated into the Brahmaputra Valley and of indigenous populations incorporated into their society over the course of history, through a process called Ahomisation. Traditional accounts place the arrival of the Tai group led by Sukaphaa in 1228 and date the foundation of the Ahom kingdom to the same year. Recent scholarship has, however, questioned this chronology, arguing that the available Tai and Chinese sources may instead indicate that the Ahom polity was established in the 14th century. Over the following centuries, the kingdom expanded across much of the Brahmaputra Valley in present-day Assam and endured until the signing of the Treaty of Yandabo in 1826.

The modern Ahom people and their culture are a syncretism of Tai and local Tibeto-Burman speakers. The mixture of immigrants and local peoples who underwent Ahomisation came to be known as Ahom. A 2004 genetic study has found that in the "tribal" and "caste" continuum, the Ahom people occupy an ambiguous position in the middle, along with the Koch-Rajbanshis and Chutias. Many local ethnic groups that came in contact with the Tai settlers, including the Borahis, were completely subsumed into the Ahom community. Members of other communities were accepted as Ahoms based on their allegiance to the Ahom Kingdom or the usefulness of their talents.

Even though the already admixed group, Ahom, made up a relatively small portion of the kingdom's population; they maintained their Ahom language and practised their traditional religion till the 17th century, when the Ahom court as well as the commoners adopted the Assamese language.

Currently, they represent the largest Tai group in India. Ahom people are found mostly in Upper Assam division in the districts of Golaghat, Jorhat, Sivasagar, Charaideo, Dibrugarh, Tinsukia (south of Brahmaputra River); and in Lakhimpur, Sonitpur, Biswanath, and Dhemaji (north) as well as some areas of Nagaon in Guwahati.

The Tai speaking people came into prominence first in the Guangxi region, in China, from where they moved to mainland Southeast Asia in the middle of the 11th century after a long and fierce battle with the Northern Han Chinese. The Tai Ahoms are traced to either Mong Mao of South China (present-day Dehong, Yunnan of China) or to the Hukawng Valley in Myanmar.

According to the traditional chronology, Sukaphaa, a Tai prince from Mong Mao, entered Assam in 1228 with a group of followers intending to establish a permanent settlement. They are traditionally believed to have brought techniques of wet-rice cultivation, a system of writing and record-keeping, and traditions of state formation. Recent scholarship has, however, questioned this chronology, proposing that the Ahom polity may instead have been founded in the mid-14th century. Linguistic research has likewise suggested that the Ahom script developed only between the late 14th century and the 16th centuries. Scholars have further argued from pre-Ahom inscriptional and Buranji evidence that settled agriculture, wet-rice cultivation and embankment-based water management had important antecedents in Assam before the Ahom entry and that groups like Kacharis already practised wet-rice cultivation when the Ahoms settled in Assam. The migrant group eventually settled in the region south of the Brahmaputra River and to the east of the Dikhow River; the Ahoms today are found concentrated in this region and established the Ahom kingdom, which over the following centuries, expanded across much of the Brahmaputra Valley until 1826.

In the initial phase, the band of followers of Sukaphaa moved about for nearly thirty years and mixed with the local population. He moved from place to place, searching for a seat. He made peace with the Borahi and Moran ethnic groups, and he and his mostly male followers married into them, creating an admixed population identified as Ahoms and initiating the process of Ahomisation. The Borahis, a Tibeto-Burman people, were completely subsumed into the Ahom fold, though the Moran maintained their independent ethnicity. Sukaphaa established his capital at Charaideo near present-day Sivasagar and began the task of state formation.

The Ahoms held the belief that they were destined by a divine force to cultivate fallow land using their wet-rice farming methods and to assimilate stateless shifting cultivators into their society. They were also conscious of their numerical minority. As a result, the Ahom polity initially absorbed Naga, Borahi and Moran, and later large sections of the Chutia and the Dimasa-Kachari peoples. This process of Ahomisation went on until the mid-16th century, when the Ahom society itself came under the direct Hindu influence. That many indigenous peoples were ceremonially adopted into Ahom clans are recorded in the chronicles. Since the Ahoms married liberally outside their own exogamous clans and since their own traditional religion resembled the religious practices of the indigenous peoples the assimilation under Ahomisation had little impediment.