  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, $Y_p$.
