The Emishi, Ebisu or Ezo (蝦夷; Japanese pronunciation: [eꜜ.mʲi.ɕi, eꜜ.bʲi.sɯ, eꜜ.(d)zo]) were a group of people who lived in parts of northern Honshū in present-day Japan, especially in the Tōhoku region.

The first mention of the Emishi in literature that can be corroborated with outside sources dates to the 5th century, in which they are referred to as máorén (毛人—"hairy people") in Chinese records. Some Emishi tribes resisted the rule of various Japanese emperors during the Asuka, Nara, and early Heian periods (7th–10th centuries).

The origin of the Emishi is disputed and continues to be a topic of discussion; however, some theories propose a connection to either the Epi-Jōmon tribes of Japan which became the ancestors of the Ainu people of Hokkaido, or pre-Yamato migrants. It has been posited that the Emishi may have either spoken a unique Japonic language similar to the Izumo dialect, or a distinct language related to Ainu, or both. Moreover, even though there is a significant geographical gap between Northeast Japan and the South—particularly Northern Kyushu, which is believed to be the initial site of rice agriculture in the archipelago—evidence indicates that local communities in northeast Japan entirely embraced rice cultivation in the early Yayoi period. This relationship could have been facilitated by human migration along the coastline of the Sea of Japan, suggesting a link between the northeast and the adoption of rice farming during the Yayoi era. A majority of scholars have also noted cultural similarities to the Ainu. The Emishi that inhabited northern Honshu consisted likely of several tribes, which included pre-Ainu people, non-Yamato, and admixed people, who united and resisted the expansion of the empire.

The first mention of the Emishi is from a Chinese source, the Book of Song in 478 CE, which referred to them as "hairy people" (毛人). The book refers to "the 55 kingdoms (國) of the hairy people (毛人) of the East" as a report by King Bu — one of the Five kings of Wa.

The first recorded use of the Japanese word Emishi is in the Nihon Shoki in 720CE, where the word appears in the phonetic spelling 愛瀰詩 for emi₁si (see also Old Japanese § Vowels for an explanation of the subscript). This is in the record of Emperor Jimmu, stating that his armed forces defeated a group of Emishi before Jimmu was enthroned as the Emperor of Japan. According to the Nihon Shoki, Takenouchi no Sukune in the era of Emperor Keikō proposed the subjugation the Emishi of Hitakami no Kuni (日高見国) in eastern Japan.

In later records, the kanji spelling changed to 蝦夷, composed of the characters for "shrimp" and "barbarian". The use of the "shrimp" spelling is thought to refer to facial hair, like the long whiskers of a shrimp, but this is not certain. The "barbarian" portion clearly described an outsider, living beyond the borders of the emerging empire of Japan, which saw itself as a civilizing influence; thus, the empire was able to justify its conquest. This kanji spelling was first seen in the T'ang sources that describe the meeting with the two Emishi that the Japanese envoy brought with him to China. The kanji spelling may have been adopted from China.

The oldest attested pronunciation emi₁si may have come from Old Japanese, perhaps from the word "yumishi" meaning "bowyer" (in reference to an important weapon, the bow), however some suggest that it came instead from the Ainu term emushi meaning "sword". The yumishi theory is problematic, as the Old Japanese term for "bowyer" was 弓削 (yuge), whereas 弓師 (yumishi) is not attested until the 1600s. Meanwhile, the later pronunciation Ebisu (derived from Emishi) was also spelled as 戎, which also means "warrior", possibly aligning with the proposed Ainu derivation via metonymy wherein the word for "sword" was used to mean "warrior".

The Emishi were represented by different tribes, some of whom became allies of the Japanese (referred to as "fushu" and "ifu") while others remained hostile (referred to as "iteki"). The Emishi in northeastern Honshū relied on horses in warfare, developing a unique style of warfare in which horse archery and hit-and-run tactics proved very effective against the slower contemporary Japanese imperial army that mostly relied on heavy infantry. The livelihood of the Emishi was based on hunting and gathering as well as on the cultivation of grains such as millet and barley. Recently, it has been thought that they practiced rice cultivation in areas where rice could be easily grown.