  I review the challenges and problems facing the standard cosmological model,
involving an $\Omega=1$ Universe dominated by non-baryonic dark matter, which
arise due to: age estimates of the universe, estimates of the baryon fraction
of the universe, and structure formation. Certain of these problems are
exacerbated, and certain of these are eased, by the inclusion of some component
to the energy density of matter from massive neutrinos. I conclude with a
comparison of the two favored current cosmological models, involving either a
mixture of cold dark matter and hot dark matter, or the inclusion of a
cosmological constant.
