Big-Bang nucleosynthesis and the universal density - constraints from the abundance of lithium

The dependence of nucleosynthesis in the Big Bang on the universal baryon density rho allows one to deduce rho from the observed isotopic abundances. One finds that the resulting baryon density is too small by a factor of 10 to close the universe. The prejudice that the universe is just closed (Omega = 1) then leads to the hypothesis that the universal mass is dominated by non-baryonic matter. This talk will review the estimates of rho with emphasis on new results for reaction rates involving mass 7 (and hence the Big Bang production of B7Li) and for the primeval abundance of 7Li based on measurements on old halo stars. These results make it possible to place plausible upper and lower bounds on the universal density based on the 7Li abundance