  I review standard big bang nucleosynthesis and some versions of nonstandard
BBN. The abundances of the primordial isotopes D, He-3, and Li-7 produced in
standard BBN can be calculated as a function of the baryon density with an
accuracy of about 10%. For He-4 the accuracy is better than 1%. The calculated
abundances agree fairly well with observations, but the baryon density of the
universe cannot be determined with high precision. Possibilities for
nonstandard BBN include inhomogeneous and antimatter BBN and nonzero neutrino
chemical potentials.
