GTI may refer to:
- Volkswagen Golf GTI, a car
- GTi Engineering, an auto racing team
- Galway Technical Institute
- Grand Tourer Injection, a car model variant
- GT Interactive, a video game publisher and distributor
- Guilford Transportation Industries, a transportation company
- GrafTech, a graphite manufacturing company, NYSE symbol GTI
- Atlas Air, ICAO code GTI
- Grid-tie_inverter, an aparatus to convert dc electrical (solar, wind) energy to ac and deliver it back to the grid.