Book excerpt: The proceedings of this workshop consideres the prospects for opening up a new window on the universe with the generation of High Energy Neutrino telescopes now under construction or being planned. Potential sources of high energy neutrinos such as binary pulsars, supernovae, and active galactic nuclei are discussed. In particular, the recent model of Stecker and collaborators, in which neutrinos with energies as high as 1000 TeV are produced in measurable quantities in the cores of quasars and other active galaxies is critically reviewed.