The physics Monte Carlo simulation of the GlueX detector is based upon an abstract model of the experimental geometry and fields expressed in the form of a hierarchy of xml documents. This geometry is converted to the internal representation of whatever simulation package is used in MC production (currently Geant3), which propagates tracks through the detector, generates hits in sensitive materials, and collects the hits at the end of each event into an output record. Representing the detector geometry in a form that is suitable for accurate and efficient simulation requires a model for each detector subsystem. Models have been assembled for each subsystem which satisfy the minimum requirements that they have the correct sensitive area coverage, the right amount and type of material at a level of detail better than the detector position resolution, and at least as much segmentation as required by the readout. This report provides a brief description of the models used for each subsystem, and describes how the detector response is simulated.
