Io

Io, IO, I/O, i/o, or i.o. may refer to:

In arts and entertainment

Io (opera), an unfinished acte de ballet (opera) by Jean-Philippe Rameau
Io (Babylon 5), a space station in the science fiction television show Babylon 5
Blind Io, the current king of the gods in Terry Pratchett's Discworld series of fantasy novels
Scylla Io, one of Poseidon's Marine Generals in the Saint Seiya series
International Operations, a fictional American Intelligence Agency in Wildstorm comics

iO Digital Cable Service, a service offered by Cablevision
IO Interactive, a Danish computer game developer
iO Theater (ImprovOlympic), a theater in Chicago, Illinois, dedicated to improvisational comedy
IO West, a Los Angeles theater associated with the Chicago iO

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

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

Io Shirai (born 1990), Japanese professional wrestler
iO Tillett Wright (borh 1985), American artist, director, photographer, writer, film maker, activist, and actor

Io (genus), a genus of freshwater snail in the family Pleuroceridae
Automeris io, a moth species in North America
Inachis io, the European Peacock butterfly
Intraosseous infusion, the medical process of introducing medication directly into the bone marrow
Hawaiian hawk, in the local dialect

.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
Input/output, the collection of interfaces that different functional units of an information processing system use to communicate with each other

Ionium (symbol Io), a claimed chemical element that was later realized to be thorium-230
Image orthicon tube, a TV camera used between 1946 and 1968

Io (voievodal title particle), a particle of a title used by Romanian royalty from Moldavia and Walachia
Mitsubishi Pajero iO, a mini SUV produced by Mitsubishi Motors
Indonesian Airlines (IATA airline designator)
International Organization, a peer-reviewed journal that covers the entire field of international affairs
Bureau of International Organization Affairs, in the U.S. Department of State
Investigating Officer, a member of law enforcement in the United Kingdom who heads an investigation