Jeffrey Hittinger - Lawrence Livermore National Laboratory, Center for Applied Scientific Computing In this talk, the motivations behind simulation will be discussed using examples from science and engineering applications. We will then overview how simulation is done, from modeling through approximation, solvers, and data analysis, including uncertainty quantification and optimization. The goal is to provide an introduction to the concepts and language common to numerical simulation. Along the way, we will discuss the challenges that are driven by the physics, the mathematics, and the HPC systems required for large-scale simulation.