Yamata no Orochi (八岐大蛇, 八俣遠呂智, 八俣遠呂知; ヤマタノオロチ),) is a legendary eight-headed and eight-tailed serpent that appears in Japanese mythology. Both the Kojiki and Nihon Shoki record that the kami Susanoo no Mikoto, in order to rescue Kushinadahime, defeated the serpent and that the Kusanagi no Tsurugi, part of the Imperial Regalia of Japan, was found within the serpent's tail.

In local tradition, Yamata no Orochi was believed to have survived their encounter with Susanoo and fled to Mount Ibuki, where they were venerated as Ibuki Daimyōjin (伊吹大明神)). Additionally, figures such as Emperor Antoku and Longnü have been identified as incarnations of Yamato no Orochi.

The name Yamata no Orochi (八俣遠呂智 in the Kojiki, 八岐大蛇 in the Nihon Shoki) is variously translated as "Eight-Forked Serpent", "Eight-Headed-Serpent" and "Eight-Headed Dragon", with orochi (大蛇) being used in modern Japanese to refer to a large snake or dragon.

Orochi is derived from the Old Japanese woröti, but its etymology is enigmatic. While Western linguists have suggested that woröti is a loanword from Austronesian, Tungusic, and Indo-European languages, the more likely etymologies put forward by Japanese scholars argue that it comes from oro (尾ろ; "tail"), ō (大; "big/great"), or dialectal oro (峰ろ; "peak/summit"), in addition to chi (霊; "god/spirit"), possibly being a cognate with mizuchi, (蛟; "water spirit/dragon") and ikazuchi (雷; "[god of] thunder").

Yamata (八岐/八俣; "eight-forks/branches") on the other hand, may be related to other instances of "eight" (八, read as either yatsu or hachi) in Japanese literature, used to mean "many" or "several", for example: yata (八咫; "long/large"), yae (八重; "many-layered") and yashima (八洲; "many islands", i.e. Japan).

The earliest record of the Yamata no Orochi myth comes from the Kojiki, the oldest extant source of Japanese mythology, completed in the year 712 by Ō no Yasumaro at the behest of Emperor Tenmu and Empress Genmei.

After being banished from Takamagahara, the god Susanoo (須佐之男) descended to a place called Torikami (鳥髪) in the land of Izumo, where he found a chopstick floating down the River Hi (簸川, known today as the Hii river). Taking this as a sign that there must be people living nearby, Susanoo traveled upstream and came across an elderly couple and a young girl, all of whom were weeping. The old man introduced himself as Ashinazuchi (足名椎), an earthly deity and child of the mountain god Ōyamatsumi. His wife was Tenazuchi (手名椎) and his daughter was Kushinada-hime (櫛名田比売). Originally the couple had eight daughters, but every year an eight-headed serpent from Koshi (高志之八俣遠呂智, Koshi no Yamata no Orochi) had appeared and devoured one of them. Now only Kushinada-hime remained and she was soon to be eaten too, for this reason the three of them wept. When questioned on the serpent's appearance, Ashinazuchi described it as such:

“Its eyes are like red cherries (赤酸醤, akakagachi) and it has eight heads and eight tails. Covered in moss, cypress and cedar, it spans eight valleys and eight peaks, and when you look at its belly you see blood oozing out everywhere.”