GTB is a three-letter acronym that can refer to:
- Guaranty Trust Bank, a bank in Nigeria and West Africa
- Genting Airport, an airport in Malaysia
- Grounded Theory Building
- Gran Turismo Berlinetta, a style of Ferrari
- Groupe de Travail "Bruxelles 1952" or Working party Brussels 1952, a group of automotive and vehicle industry lighting experts who contribute to the World Forum for Harmonization of Vehicle Regulations
- Grand Theft Bus, a Canadian indie rock band
- Google Toolbar
- Guru Tegh Bahadur, the 9th Guru of Sikhism.
- Go Time Boys, an elite private members club founded in London