As mentioned in the introduction to this book, Chamberlin (1933) contributed significantly to the development of economists’ interest in the role played by product differentiation in the analysis of the functioning of markets. Not only did he draw the attention of the latter to this role, but he also proposed a theoretical approach that has been revived in recent years because of the numerous applications of this approach in several fields of economic science, such as the theory of international trade or geographic economics. It would not be acceptable not to mention this approach in the context of this book, even if it contrasts singularly with the one pioneered by Hotelling.