  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. The physical effects
relevant at these widely separated epochs are reviewed and the theoretical
predictions are compared with observational data to explore the consistency of
the standard models of cosmology and particle physics and to constrain
beyond-the-standard-model physics and cosmology.
