OO, O_O or variants may refer to:
Arts and entertainment OO (EP), by Zion.T, 2017 "O.O" (song), by Nmixx, 2022 The Ice Warriors, a 1967 Doctor Who serial (production code OO)
Language <oo>, a Latin-script digraph , a ligature of the Latin script
People Oo Zun (1868–1944), Burmese social worker and Buddhist nun Tin Oo (1927–2024), Burmese politician, activist and military
Places Oô, France Oo, Indonesia Old Oak Common TMD, England, carriage shed depot code OO Belgium (aircraft registration prefix OO)
Other uses Ōō, an extinct bird of the genus Moho Oo stick, a traditional Hawaiian digging bar OO gauge, a model railway standard Official Observer, an appointed amateur radio operator Several emoticons Oriental Orthodoxy, a Christian denomination Original Oratory, a competitive event in high school forensic competitions SkyWest Airlines, IATA airline code OO
See also Double O (disambiguation) 00 (disambiguation) 0-0 (disambiguation) O0 (disambiguation) OOO (disambiguation) , infinity symbol ᅇ, an obsolete unit of the Hangul alphabet ⚭, marriage symbol ⱺ, a phonetic character Object-oriented programming, a computer programming paradigm Orange Order, a protestant fraternal order in Northern Ireland , mathematical notation for zero to the power of zero