The role of neutrino masses and mixing in the astrophysical and cosmological context is reviewed. If neutrino mass differences are indeed as small as suggested by the current evidence for neutrino oscillations (Δ mν ≪ 1 eV), the overall neutrino mass scale in scenarios of degenerate neutrino masses is the most challenging open issue. Cosmological structure-formation arguments will continue to provide the most restrictive limits unless neutrinoless ββ experiments find positive evidence for a sub-eV mass scale. Neutrino Majorana masses in the range suggested by current oscillation experiments are fundamentally important in leptogenesis scenarios for creating the matter-antimatter asymmetry of the universe. The existence of a sterile neutrino, as suggested by the current evidence for neutrino oscillations, could affect big-bang nucleosynthesis as well as r-process nucleosynthesis in the neutrino-driven wind of type II supernovae. If the solar neutrino problem is explained by large-angle oscillations, a significant modification of the detectable signal characteristics of a future galactic SN is inevitable. The oscillation interpretation of the atmospheric neutrino anomaly suggests that the high-energy neutrino fluxes expected from cosmic beam dumps will have a large ν τ component.