IRT may refer to:
- Immunoreactive trypsinogen, used as a newborn screening test for cystic fibrosis
- Indiana Repertory Theatre, a theatre in Indianapolis, Indiana
- Infrared thermography
- Institut für Rundfunktechnik, the research institute of the public broadcasters of Germany, Austria, and Switzerland
- Interborough Rapid Transit Company, former operator of a portion of the New York City Subway system
- Isochronous real time, a computer protocol used for PROFINET IO
- Item response theory, a theory to interpret data from psychometric tests
- Ice Road Truckers, a documentary television series on History Channel
- IRT: Deadliest Roads, a spin-off series of Ice Road Truckers