Two-way satellite time and frequency transfer (TWSTFT) is a high-precision long distance time and frequency transfer mechanism used between time bureaux to determine and distribute time and frequency standards.

As of 2003^[update] TWSTFT is being evaluated as an alternative to be used by the Bureau International des Poids et Mesures in the determination of International Atomic Time (TAI), as a complement to the current standard method of simultaneous observations of GPS transmissions.