DOI or Doi may refer to:
- Doi (surname), a Japanese surname
- Doi (retailer), a Japanese company
- 2,5-Dimethoxy-4-iodoamphetamine, a hallucinogenic drug
- Digital object identifier, an international standard for document identification
- Distinctness of image, a quantification of vision used in optics
- Division of Investigation, a precursor to the U.S. Federal Bureau of Investigation
- Dogri language (ISO 639 code), spoken in India and Pakistan
- New York City Department of Investigation, law enforcement agency
- United States Department of the Interior, an executive department of the U.S. government
are three Japanese family names that are pronounced identically, with the first kanji of each pair of characters meaning "earth." Since they are the same phonetically, they are romanized identically: "do" for the first character and "i" for the second. Their identical pronunciation makes them function as the same surname in languages with writing systems that do not use some form of Chinese characters (for example, the Latin alphabet).
was a large Japanese retailer and distributor, best known outside Japan as the company that revived the Plaubel Makina 67 camera in the late 1970s and early 1980s.
Its roots go back to Doi Shōten , also referred to as Doi Shōkai . This was a Japanese retailer, distributor, or both, that started in 1949. (Doi here is a surname, shōten means "retailer", and shōkai means "trading company".) In the early fifties it was based in Osaka.
Kimio Doi (, Doi Kimio), son of the Mr. Doi of Doi Shōten, started a branch in Fukuoka at some time around 1956. In 1959 this became plain Doi (, Kabushiki Kaisha Doi).
Doi provided diverse services, such as professional darkroom work. Retail stores were branded "Camera no Doi" (, Kamera no Doi); these were known for the array of used cameras as well as competitive prices of new equipment.
By the 1980s, Doi was as large a presence as Yodobashi Camera in the Nishi-Shinjuku area of west-central Tokyo. Its sales peaked in March 1989. However, it faltered in the 1990s and closed down in 2003. Doi Technical Photo seems to have survived this, even running a photography gallery in Yūrakuchō, but now (2006) appears to be defunct.