  Big Bang Nucleosynthesis (BBN) and the Cosmic Background Radiation (CBR)
provide complementary probes of the early evolution of the Universe and of its
particle content. Neutrinos play important roles in both cases, influencing the
primordial abundances of the nuclides produced by BBN during the first 20
minutes as well as the spectrum of temperature fluctuations imprinted on the
CBR when the Universe is some 400 thousand years old. In this talk I review the
physical effects of neutrinos at these different epochs in the evolution of the
Universe and compare the theoretical predictions with the observational data to
explore the consistency of the standard models of cosmology and particle
physics and to constrain neutrino physics as well as more general,
beyond-the-standard-model physics.
