We review numerical simulations of galaxy clusters with an emphasis on cosmological basics, numerical methodologies, and recent results. The following topics are covered: the standard cosmological framework, growth of perturbations in the linear regime, analytic models for nonlinear perturbation growth, statistics of galaxy cluster populations, virial scaling relations, overview of numerical methods, simulating gas in galaxy clusters, basic results on adiabatic clusters (Santa Barbara cluster comparison project), effect of additional physics, recent progress in galaxy clustering modeling (Galcons, turbulence, AGN jets, cluster-wide B-fields), simulating statistical samples and lightcones, and simulated SZE surveys.