Big Bang Nucleosynthesis and Dark Matter: Baryons and Neutrinos

I present a review of Big Bang Nucleosynthesis, concentrating on the statistical analysis of theoretical uncertainties, and on systematic errors in observed abundances. Both have important implications for constraints on the amount of baryonic dark matter and the number of light neutrino species in nature. Without allowing for systematic uncertainties in abundances, we find that homogenous BBN would lead to the constraint $\Omega_B \le .07$ and $N_{\nu} \le 3.07$. Even allowing for maximal systematic uncertainties in $^4$He, and $^7$Li, we find $\Omega_B \le .163$. For intermediate ranges we provide new analytic fits for the upper limits to $N_{\nu}$ and $\Omega_B$ as a function of the helium mass fraction, $Y_p$.