A spatial simulation model of annual plant interference which employs dispersal and neighborhood effects is developed and implemented with a computer program. The following hypotheses are observed to be consistent with the behavior of the model: 1. (1) Dispersal rates are extremely important in determining the rate at which a species can colonize or eleminate an inferior competitor from an area. 2. (2) Dispersal rates and local competition result in spatial patterns in plant populations which retard or prevent competitive elimination under conditions where it would be expected from non-spatial models. If interspecific competition is more intense than intraspecific competition, a mosaic of patches each dominated by one species will develop, but these patches may be in equilibrium. The inclusion of space in a plant competition model, even in a crude way, results in behavior which is significantly different from that of non-spatial models.