  High energy neutrino astrophysics has come of age with the discovery by
IceCube of neutrinos in the TeV to PeV energy range attributable to
extragalactic sources at cosmological distances. At such energies,
astrophysical neutrinos must have their origin in cosmic ray interactions,
providing information about the sources of high energy cosmic rays, as well as
leading to the co-production of high energy gamma-rays. The intimate link with
these latter two independently observed types of radiation provides important
tools in the search for identifying and understanding the nature of their
astrophysical sources. These neutrinons can provide important constraints about
the cosmic ray acceleration process, and since they travel essentially
unimpeded they can probe our Universe out to the farthest cosmological
distances.
