Computation has assumed a status equal in importance to theory and experiment in many science and engineering disciplines. Computational science and engineering is now recognized as a specialty that is well served by neither a traditional degree in computer science nor a science or engineering degree. Scientists wishing to contribute through large-scale computation to leading edge research must henceforth have a background that includes a significant share of the course requirements of both types of degrees, and integrates computing with a science or engineering discipline. Problems that are ``simple" enough to be addressed through analytical models alone, or analyzed through a limited battery of experiments, have become few and sparse. Most remaining addressable problems involve considerable complexity, and are best approached through a combination of modes of investigation that includes skillful computational simulation.