This paper provides a framework to understand how market size affects firms' investments in product differentiation in a model of monopolistic competition. The theory proposes that consumers' love of variety makes them more sensitive to product differentiation efforts by firms, which leads to more differentiated products in larger markets. The framework also predicts an inverted -shaped effect of trade liberalization on product differentiation, with trade liberalization leading to more differentiated products when starting from autarky but then leading to less differentiated products as the countries approach free trade.

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.

This paper sets up a model of endogenous product differentiation to analyze the variety effects of international trade. In our model multi-product firms decide not only about the number of varieties they supply but also about the degree of horizontal differentiation between these varieties. Firms can raise the degree of differentiation by investing variety-specific fixed costs. In this setting, we analyze how trade integration, i.e. an increase in market size, influences the number of firms in the market, the number of product varieties supplied by each firm, and the degree of differentiation.

We study how firms differ from their competitors using new dynamic measures of product differentiation based on novel text based analysis of 50,673 product descriptions from firm 10-K statements filed yearly with the Securities Exchange Commission. This year-by-year set of firm product differentiation measures allows us to generate a set of dynamic industry classifications and new measures of industry structure and competition. Competitiveness and market structure measures based on these new classifications better correlate with firm profitability than do classifications based on SIC or NAICs. Using these new dynamic industry classifications, we examine endogenous product differentiation. We show that firms use R & D and advertising to differentiate themselves from competitors and increase their profitability.