In order to alleviate the high costs and inflexibility associated with full-scale fire tests which are commonly employed to predict the fire resistance of wood-frame building assemblies, the North American wood industry has identified the need for computer models to calculate fire resistance. The two-dimensional computer model presented in this report simulates fire tests for gypsum-board/wood-stud wall assemblies. In such assemblies, the gypsum board acts mainly as a protective membrane and it provides much of an assembly's fire resistance. The primary advantage of the two-dimensional computer model as opposed to its one-dimensional predecessor is that, in addition to predictions of heat transfer through gypsum board attached to wood studs, it also predicts heat transfer through the wall's cavity. Thermophysical properties of both gypsum and wood were reviewed before being incorporated in the model. Along with the added dimension mentioned earlier, other interesting features of this model include its consideration of linear expansion (contraction) of gypsum and the considerable effect of charring of wood which ultimately affects all of the latter's thermophysical properties. Simulation results obtained using the model are remarkably accurate when compared to full- and small-scale fire tests. The aforementioned tests were performed at the National Fire Laboratory (NFL) to provide data for the validation of the model. A brief overview of the sensitivity analyses which were performed on the model is also included in this report.