There are few industries in modern market economies that do not manufacture differentiated products. This book provides a systematic explanation and analysis of the widespread prevalence of this important category of products. The authors concentrate on models in which product selection is endogenous. In the first four chapters they consider models that try to predict the level of product differentiation that would emerge in situations of market equilibrium. These market equilibria with differentiated products are characterised and then compared with social welfare optima. Particular attention is paid to the distinction between horizontal and vertical differentiation as well as to the related issues of product quality and durability. This book brings together the most important theoretical contributions to these topics in a succinct and coherent manner. One of its major strengths is the way in which it carefully sets out the basic intuition behind the formal results. It will be useful to advanced undergraduate and graduate students taking courses in industrial economics and microeconomic theory.

Spatial quality choice is introduced, where consumers are horizontally differentiated by taste and firms vertically differentiated by quality location, within an equilibrium model of duopoly competition characterized by asymmetric fixed and variable costs. Firms choose quality location followed by prices but then may vertically re-locate their quality offerings based on changing horizontal consumer taste. A monopolistic equilibrium solution arises with firms achieving positive economic profits through price-quality markups exceeding marginal costs. Under strict inequality conditions, each firm acts as a monopolistic competitor within a range of quality choices governed by multiple relative differentiation outcomes. On the other hand, vertical re-location exhibits a resistance to change on the part of vertically located firms such that firms dislike quality re-location and prefer stable preferences in quality. Such resistance to change is overcome by firms re-locating their quality offerings to maximize monopolistic brand-space gains. It is argued that more horizontal differentiation may force more product differentiation by vertical quality relocation. A relative change in quality preferences may result in wider quality spreads in the market through vertical quality re-locations, even though the resistance to change arguments may still hold good.