OO

OO or oo may refer to:

Science and technology

 * ‘Ō‘ō, an extinct bird of the genus Moho
 * Object-oriented programming, a computer programming paradigm
 * O.O (also O.o or o.O), an emoticon to represent two eyes and a nose or mouth

Transportation

 * SkyWest Airlines (IATA code: OO)
 * Belgium (aircraft registration prefix: OO)
 * Old Oak Common TMD, a carriage shed (Network Rail depot code: OO)

Places

 * Oô, a commune in France
 * Oo, Indonesia

Art and entertainment

 * OO (EP), album by South Korean singer Zion.T
 * OO, the production code for the 1967 Doctor Who serial The Ice Warriors

Other uses

 * Oo (digraph), a digraph in orthography
 * ‘O‘o stick, a traditional Hawaiian digging bar
 * Original Oratory, a competitive event in high school forensic competitions
 * Oakley, Inc. (NYSE stock ticker symbol: OO), subsidiary of Italian company Luxottica
 * OO gauge, a 1:76.2 modelling scale in model railroading
 * Official Observer, an appointed amateur radio operator