Neutrinos and primordial nucleosynthesis

The importance of the Big Bang Nucleosynthesis (BBN) as a unique tool for studying neutrino properties is discussed, and the recent steps towards a self-consistent and robust handling of the weak reaction decoupling from the thermal bath as well as of the neutrino reheating following the e(+) - e(-) annihilation are summarized. We also emphasize the important role of the Cosmic Microwave Background (CMB) anisotropy in providing an accurate and independent determination of the baryon density parameter w(b). The BBN is presently a powerful parameter-free theory that can test the standard scenario of the neutrino decoupling in the early Universe. Moreover it can constrain new physics in the neutrino sector. The perspectives for improvements in the next years are outlined.