  Astrophysical and cosmological arguments and observations give us the most
restrictive constraints on neutrino masses, electromagnetic couplings, and
other properties. Conversely, massive neutrinos would contribute to the cosmic
dark-matter density and would play an important role for the formation of
structure in the universe. Neutrino oscillations may well solve the solar
neutrino problem, and can have a significant impact on supernova physics.
