Abstract: Perfect competition provides a model of a frictionless economy in which economic agents behave independently of each other, abandoning to the market the task of coordinating their individual decisions. This model is extensively studied in traditional price theory textbooks.Imperfect competition is the paradigm that develops when, on the contrary, economic agents interact in a conscious manner, which is necessarily the case when competition takes place ‘among the few’. In this system, agents act strategically, taking into account the impact of their own decisions on competitors ‘behaviour and on the price mechanism. Such situations commonly arise when firms differentiate their products, erect strategic entry barriers, or exploit the imperfect information of their customers about the price or characteristics of their product.This book explores the theoretical richness of these economic contexts, using some basic concepts of game theory. The four assumptions underlying the paradigm of perfect competition (no barriers to entry, large number of agents, product homogeneity, and perfect information) constitute the natural departure points of the theories of imperfect competition: whenever at least one of these assumptions is violated, imperfect competition is present. The framework of the book is organized around the four corresponding themes: the role of collusion and entry barriers in the degree of market competition (Ch. 3), product differentiation (Ch. 4) and the information of agents as an instrument of competition (Ch. 5). Finally, Ch. 6 illustrates the possibility of extending the theory to a general equilibrium framework.

Keywords: barriers to entry, collusion, economic agents, game theory, general equilibrium, imperfect competition, imperfect information, oligopoly, product differentiation