  Background induced by neutrons in deep underground laboratories is a critical
issue for all experiments looking for rare events, such as dark matter
interactions or neutrinoless 2-beta decay. Neutrons can be produced either by
natural radioactivity, via spontaneous fission or (alpha,n) reactions, or by
interactions initiated by high-energy cosmic rays. In all underground
experiments, Monte Carlo simulations of neutron background play a crucial role
for the evaluation of the total background rate and for the optimization of
rejection strategies. The Monte Carlo methods that are commonly employed to
evaluate neutron-induced background and to optimize the experimental setup, are
reviewed and discussed. Focus is given to the issue of reliability of Monte
Carlo background estimates.
