Astrophysical Sources of High Energy Neutrinos in the IceCube Era

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.