The IceCube Neutrino Observatory is a detector consisting of a billion tons of ice at the geographic South Pole instrumented with thousands of photomultiplier tubes to detect neutrinos from GeV to EeV energies.  In addition to neutrino physics measurements, IceCube discovered a substantial flux of astrophysical neutrinos in the TeV to PeV energy range.  So far this flux is detected as a nearly isotropic glow, and resolving it into individual sources (neutrino astronomy) is just beginning.  There is evidence that the neutrinos are produced by at least one distant galaxy powered by a massive black hole.  But there must be at least hundreds of sources of the astrophysical neutrino flux, and likely multiple source classes.  Along with gravitational waves, detection of this signal has launched a new era of multi-messenger astrophysics, in which these new messengers complement the traditional astronomical messenger (the photon).  I will summarize our current understanding of astrophysical neutrinos, the search for their origins, and the role of neutrino astronomy in the multi-messenger context.