  A critical review is given of the current status of cosmological
nucleosynthesis. In the framework of the Standard Model with 3 types of
relativistic neutrinos, the baryon-to-photon ratio, $\eta$, corresponding to
the inferred primordial abundances of deuterium and helium-4 is consistent with
the independent determination of $\eta$ from WMAP observations of anisotropies
in the cosmic microwave background. However the primordial abundance of
lithium-7 inferred from observations is significantly below its expected value.
Taking systematic uncertainties in the abundance estimates into account, there
is overall concordance in the range $\eta = (4.7 - 6.5) x 10^{-10}$ @ 95% c.l.
(corresponding to a cosmological baryon density $\Omega_B h^2$ = 0.017 -
0.024). The D and He-4 abundances, together with the CMB determination of
$\eta$, provide the bound $N_\nu = 3.24 \pm 1.2$ @ 95% c.l. on the effective
number of neutrino species. Other constraints on new physics are discussed
briefly.
