SimLab, a software environment for creating simulators directly from computer-readable physics models, is based on the following concept: creating physical systems simulators should be as simple as describing the underlying physics to a colleague. Rather than programming in a conventional programming language, a SimLab user expresses physics models (and thus simulators) directly in terms of the concepts, quantities, and equations familiar to a scientist or engineer. The benefits of the SimLab approach include: 1) reducing the time and effort required to create simulators, 2) providing more understandable and reliable simulators, and 3) support for more sophisticated simulators, e.g., for multiple domain problems, which have proved intractible in the past.