Multiproduct Firms and Product Differentiation: a Survey.

We start the survey by reviewing the implications of horizontal and vertical product differentiation on market structure under the assumption of single-product firms. Then, we analyze the main results of the multi-product firm models, both when variants are assumed differentiated in vertical attributes only and when variants are assumed differentiated in two dimensions (vertical and horizontal). Finally, we review the empirical literature about the discrete-choice models of product differention.