TDT may refer to:
- TDT (TV station), a digital television station in Tasmania, Australia
- Terminal deoxynucleotidyl transferase, a specialized DNA polymerase expressed in immune cells
- Terrestrial Dynamical Time, an obsolete name for Terrestrial Time
- Time domain transmissometry, a method of testing transmission lines
- Toronto Dance Theatre
- Transmission disequilibrium test, a family-based genetic association test