  Excellent computer simulations are done for a purpose. The most valid
purposes are to explore uncharted territory, to resolve a well-posed scientific
or technical question, or to make a design choice. Stand-alone modeling can
serve the first purpose. The other two goals need a full integration of the
modeling effort into a scientific or engineering program.
  Some excellent work, much of it related to the Department of Energy
Laboratories, is reviewed. Some less happy stories are recounted.
  In the past, some of the most impressive work has involved complexity and
chaos. Prediction in a complex world requires a first principles understanding
based upon the intersection of theory, experiment and simulation.
