  Big Bang Nucleosynthesis is the theory of the production of the the light
element isotopes of D, He3, He4, and Li7. After a brief review of the essential
elements of the standard Big Bang model at a temperature of about 1 MeV, the
theoretical input and predictions of BBN are discussed. The theory is tested by
the observational determinations of the light element abundances and the
current status of these observations is reviewed. Concordance of standard model
and the related observations is found over a limited range of the
baryon-to-photon ratio, the single true parameter of the standard model.
Implications of BBN on chemical evolution, dark matter and constraints on
particle properties will be also discussed.
