Item response theory (IRT) has proven to be a very powerful and useful measurement tool. However, most of the IRT models that have been proposed, and all of the models commonly used, require the assumption of unidimensionality, which prevents their application to a wide range of tests. The few models that have been proposed for use with multidimensional data have not been developed to the point that they can be applied in actual testing situations. The purpose of this report is to present a model for use with multidimensional data and to discuss some of its characteristics. This discussion will include information on the interpretation of the model parameters, the sufficient statistics for the model parameters, and the information function for the model. In addition, the estimation of the parameters of the model using the maximum likelihood estimation technique is also discussed. (Author/PN)