Irezumi is any of several forms of traditional Japanese tattooing, along with certain modern forms derived from or inspired by these.

In Japanese, the word can be written in several ways, each with slightly different connotations. The most common way of writing irezumi is with the Chinese characters 入れ墨 or 入墨, literally meaning to "insert ink". The characters 紋身 (also pronounced bunshin) suggest "decorating the body". 剳青 is more esoteric, being written with the characters for "stay" or "remain" and "blue" or "green", and probably refers to the appearance of the main shading ink under the skin. 黥 (meaning "tattooing") is rarely used, and the characters 刺青 combine the meanings "pierce", "stab", or "prick", and "blue" or "green", referring to the traditional Japanese method of tattooing by hand.

Tattooing for spiritual and decorative purposes in Japan is thought to extend back to at least the Jōmon or paleolithic period (approximately 10,000 BC). Some scholars have suggested that the distinctive cord-marked patterns observed on the faces and bodies of figures dated to that period represent tattoos, but this claim is by no means unanimously accepted. There are similarities, however, between such markings and the tattoo traditions observed in other contemporaneous cultures.

In the following Yayoi period (c. 300 BC–300 AD) tattoo designs were observed and remarked upon by Chinese visitors. Such designs were thought to have spiritual significance as well as functioning as a status symbol.

Starting in the Kofun period (300–600 AD) tattoos began to assume negative connotations. Instead of being used for ritual or status purposes, tattooed marks began to be placed on criminals as a punishment.