Observations by the HAWC, H.E.S.S. and LHAASO telescopes have detected bright, spatially extended, and hard-spectrum gamma-ray emission surrounding populations of young and middle-aged pulsars. The intensity of these sources indicates that pulsars efficiently convert a significant fraction of their spin-down power into the production of relativistic electron and positron pairs. Moreover, the surface brightness of this emission indicates that the e+e− pairs remain trapped in a ∼20 pc region surrounding the pulsar for a considerable time – an observation that indicates that the diffusion constant surrounding energetic sources is significantly suppressed. Excitingly, recent observations have indicated that these sources continue to produce intense emission to energies exceeding 100 TeV. We discuss the current state of this field, and the potential for TeV halos to become a new tool capable of studying the most extreme processes in our universe.