Publication costs assisted by Bell Laboratories Theoretically, the state of the art is in excellent shape. A two-phase scheme consisting of spatial discretization followed by time discretization has been proven to converge for virtually every classical, textbook form of time-varying partial differential equation known. The time discretization is accomplished by "stiff' differential equation solvers which are robust, efficient, and easy to use. In one space variable, the spatial discretization is well understood and there are several robust and efficient schemes available. In general, for problems with more than one space variable, the spatial discretization schemes are not well understood at all. The reasons for this are discussed and possible alternative spatial discretization schemes are outlined.