  I give a brief critical review of the predicted intensity of diffuse high
energy neutrinos of astrophysical origin over the energy range from 10^12 eV to
10^24 eV. Neutrinos from interactions of galactic cosmic rays with interstellar
matter are guaranteed, and the intensity can be reliably predicted to within a
factor of about 2 up to 10^17 eV. Somewhat less certain are intensities in the
same energy range from cosmic rays escaping from normal galaxies or active
galactic nuclei (AGN) and interacting with intracluster gas. At higher
energies, neutrinos will be produced by interactions of extragalactic cosmic
rays with the microwave background. Other sources, such as AGN, in particular
blazars, and topological defects, are more speculative. However, searches for
neutrinos from all of these potential sources should be made because their
observation would have important implications for high energy astrophysics and
cosmology.
