  Big bang nucleosynthesis (BBN), an epoch of primordial nuclear
transformations in the expanding Universe, has left an observable imprint in
the abundances of light elements. Precision observations of such abundances,
combined with high-accuracy predictions, provide a nontrivial test of the hot
big bang and probe non-standard cosmological and particle physics scenarios. We
give an overview of BBN sensitivity to different classes of new physics: new
particle or field degrees of freedom, time-varying couplings, decaying or
annihilating massive particles leading to non-thermal processes, and catalysis
of BBN by charged relics.
