Long predicted but first directly detected only in 2000, tau neutrinos have played important roles in our understanding of neutrino oscillation phenomena. After a review of neutrino properties, this colloquium will focus on two opportunities to use tau neutrinos to enhance our understanding in particle physics and particle astrophysics. The first topic is the proposed Forward Physics Facility, where tau neutrinos are produced in high energy collisions at the Large Hadron Collider. We then turn to the physics and astrophysics potential of Earth-skimming tau neutrinos.