Lake, G.Quinn, T.Richardson, D. C.Stadel, J.We describe the keys to meeting the challenges of N-body simulation: adaptive potential solvers, adaptive integration, and volume renormalization. With these techniques and a dedicated teraflop facility, simulation can keep pace with observations of the universe. We also describe some problems in simulating the formation and stability of planetary systems.en-USplanetary systemsN-body simulationArticle