Simulations of clusters of galaxies reveal how clusters form and evolve. Models of cluster mergers show many characteristics of these very energetic events: shock structure and strength, temperature variations and gas distribution. Also detailed observational signatures of the dynamical state can be derived from the models. The simulations show that mergers have effects on the magnetic field, on the X-ray luminosity, on mass determination, on metal enrichment processes and other physical processes in clusters of galaxies.