Excellence in computer simulation

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 good 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 US Department of Energy´s laboratories, is reviewed. Some less happy stories are recounted.