# Io

Io most commonly refers to:
* Io (moon), a moon of Jupiter
* Io (mythology), daughter of Inachus in Greek mythology, and lover of Zeus who was turned into a cow
Io, IO, iO, I/O, i/o, or i.o. may also refer to:

## Arts, entertainment and media
### Fictional elements

* Scylla Io, one of Poseidon's Marine Generals in the Saint Seiya series
* A Dungeons & Dragons dragon deity
* Io Otonashi, a main character in the Japanese manga series Place to Place (Acchi Kocchi)
* Io Nitta, a character in the game Shin Megami Tensei: Devil Survivor 2

### Gaming

* iO, a 2014 video game by Gamious
* IO Interactive, a Danish computer game developer

### Music

* IO (German band), a German band
* Io (English band), an English band
* I_o (musician), an American DJ and record producer (1990–2020)
* i/o (Peter Gabriel album), 2023

### Theatre and opera

* Io (opera), an unfinished acte de ballet (opera) by Jean-Philippe Rameau
* iO Theater (ImprovOlympic), a theater in Chicago, Illinois, dedicated to improvisational comedy
* IO West, a Los Angeles theater associated with the Chicago iO

### Other uses in arts, entertainment and media

* EO (original Polish title: IO), a 2022 Jerzy Skolimowski film
* Io (film), a 2019 Netflix film
* iO Digital Cable Service, a service offered by Cablevision
* International Organization, a peer-reviewed journal that covers the entire field of international affairs

## Business and economics

* Industrial and organizational psychology, the field of psychology that studies work, academic, and other organizational issues
* Industrial organization, the field of economics that studies the strategic behavior of firms, the structure of markets and their interactions
* Insertion order, a business document specifying the inventory goal of an advertising campaign
* Integrated operations, a term used in the petroleum industry describing new work processes and ways of working that have been facilitated by modern information and communication technologies
* Interest-only, a type of collateralized mortgage obligation (CMO) or mortgage-backed security

## Language

* i.o., in illo ordine, Latin phrase meaning "respectively" ("in that order")
* Io (princely title), a particle of a title used by Moldavian and Wallachian Princes-regnant
* Ido language (ISO 639-1 language code IO), a constructed language
* Indirect object, the object that is the recipient of an action (by a verb)
* Yo, also referred to as Io

## Mythology

* Io (mythology), daughter of Inachus in Greek mythology, and lover of Zeus who was turned into a cow
* Io, an alternate spelling of the nereid Ino, later known as Leukothea, who in the Odyssey gave Odysseus a veil that allowed him to breathe underwater
* Io Matua Kore, in some Māori traditions the supreme god

## People

* Io Murota (室田 伊緒, born 1989), Japanese shogi player
* Io Sakisaka (咲坂 伊緒), Japanese manga artist
* Io Shirai (born 1990), Japanese professional wrestler
* Iou Kuroda (黒田 硫黄, born 1971), Japanese manga artist
* iO Tillett Wright (born 1985), American artist, director, photographer, writer, film maker, activist, and actor

## Places on Earth

* British Indian Ocean Territory, ISO 3166-1 alpha-2 code
* Io (island), an uninhabited islet near Crete, Greece
* Io, Norway, a village in Alver, Norway
* Mount Iō (disambiguation), name of several mountains in Japan
* Indian Ocean

## Science and technology
### Astronomy

* Io (moon), a moon of Jupiter
* 85 Io, an asteroid

### Biology and medicine

* Io (gastropod), a genus of freshwater snail in the family Pleuroceridae
* Io (plant), a genus of plant in the tribe Senecioneae
* Automeris io, a moth species in North America
* Aglais io, the European peacock butterfly
* Intraosseous infusion, the medical process of introducing medication directly into the bone marrow
* Hawaiian hawk (Hawaiian: ʻio)
* Immuno-oncology, another term for cancer immunotherapy

### Computing

* .io, the Internet country code top-level domain (ccTLD) for the British Indian Ocean Territory
* Io (programming language), a pure object-oriented programming language
* IO.SYS, a system file in Microsoft DOS and Windows 95, 98 and ME
* Indistinguishability obfuscation, a cryptographic tool to obscure computer code
* Input/output, the collection of interfaces that different functional units of an information processing system use to communicate with each other

### Other uses in science and technology

* Ionium (symbol Io), a claimed chemical element that was later realized to be thorium-230
* Iodine monoxide (symbol IO)
* Image orthicon tube, a TV camera used between 1946 and 1968
* Infinitely often, a mathematics term sometimes written "i.o."; see an example in set-theoretic limit

## Other uses

* Bureau of International Organization Affairs, in the U.S. Department of State
* Government Printing Bureau (Macau), known in Portuguese as the Imprensa Oficial or "IO"
* Indonesian Airlines (IATA airline designator IO)
* Investigating Officer, a member of law enforcement in the United Kingdom who heads an investigation
* Mitsubishi Pajero iO, a mini SUV model produced by Mitsubishi Motors
* IO (Oral-B), a series of electric toothbrushes by Oral-B