GRBs have redshifts comparable to, perhaps even larger than those of quasars. Indeed, they are the most energetic explosions in the universe, with energies of orderM⊙c2.Their host galaxies are faint, but are actively forming stars at rates typical of galaxies in the early universe. The current paradigm associates GRBs with the formation of black holes in massive, rotating stars, or with the mergers of compact binaries. GRBs thus trace the cosmic star formation rate and may be the most easily detectable emission of the earliest generation of stars. ©2000 American Institute of Physics.