The ambition of the theory of imperfectly competitive markets is to explain the working of markets in which the issue of strategic interaction among firms is central. Our analysis of this problem will be based on equilibrium concepts borrowed from Game Theory. This research program arises several questions on its feasibility like the empirical relevance of the results, the substantial theoretical insights obtained in this way, etc. Unfortunately, most of these questions can not be answered in the short run. This book is written in the hope that this research strategy is meaningful, but about...