STO may refer to:
- Seoul Tourism Organization The Seoul Tourism Organization
- Service du travail obligatoire, a forced labour programme introduced by the Vichy French government during World War II
- Slater-type orbital, a function used to describe atomic orbitals in quantum chemistry
- Société de transport de l'Outaouais, a public transit operator in Gatineau, Quebec, Canada
- Sojourner Truth Organization, a defunct American leftist group
- Soldiers of the One, a monotheistic religious group in Syfy's Caprica
- Space Tornado Ogawa, a professional wrestling throw
- SportsTime Ohio, a regional sports network in northeast Ohio, United States
- Star Trek Online, a massively multiplayer online role-playing game
- State Trading Organization, a publicly owned Maldivian company
- Statoil, a publicly traded Norwegian oil company
- STO-nG basis sets, the minimal basis sets in numeric quantic chemistry
- STO - Brooklyn-based artist
- Stockholm-All Airports, IATA airport code for Stockholm, Sweden including Arlanda Airport (ARN), Skavsta Airport (NYO), Bromma Airport (BMA), Västerås Airport (VST)
- Stoney language (ISO 639-3 code)
- Strontium titanate (SrTiO3)