  Primordial or big bang nucleosynthesis (BBN) is now a parameter free theory
whose predictions are in good overall agreement with observations. However, the
7Li calculated abundance is significantly higher than the one deduced from
spectroscopic observations. Most solutions to this lithium problem involve a
source of extra neutrons that inevitably leads to an increase of the deuterium
abundance. This seems now to be excluded by recent deuterium observations that
have drastically reduced the uncertainty on D/H and also calls for improved
precision on thermonuclear reaction rates.
