Parallel computers with large storage capacities have paved the way for increasing both the fidelity and complexity of large-scale simulations.  Increasing fidelity leads to tighter constraints on time steps for stability of explicit methods.  Increasing complexity tends to also increase the number of physics models and variations in time scales.  Providing both a stable solution process which can accurately capture nonlinear coupling between dynamically relevant phenomena while stepping over fast waves or rapid adjustments leads us toward implicit solution approaches.   This presentation provides an overview of issues arising in large- scale, multiphysics simulations and some of the motivators for looking at implicit approaches.  We discuss several popular implicit nonlinear solver technologies and show examples of uses of them within the context of problems found in supernova, subsurface simulation, fusion, and nonlinear diffusion problems.