  Primordial nucleosynthesis provides a probe of the Universe during its early
evolution. Given the progress exploring the constituents, structure, and recent
evolution of the Universe, it is timely to review the status of Big Bang
Nucleosynthesis (BBN) and to confront its predictions, along with the
constraints which emerge from them, with those derived from independent
observations of the Universe at much later epochs in its evolution. Following
an overview of the key physics controlling element synthesis in the early
Universe, the predictions of BBN in the standard models of cosmology and
particle physics are presented, along with those from some non-standard models.
The observational data used to infer the primordial abundances are described,
with an emphasis on the distinction between precision and accuracy. The
observationally inferred relic abundances are compared with the predicted
abundances, testing the internal consistency of BBN and enabling a comparison
of the BBN-inferred constraints with those derived from the Cosmic Background
Radiation and Large Scale Structure data. Emerging from these comparisons is
confirmation of a successful standard model along with constraints on (or hints
of) physics beyond the standard models of particle physics and of cosmology.
