We try to understand why firms producing goods by means of complementary components do not merge, especially in industries in which investments in component-based knowledge matters. As Audretsch, we state that these activities are developed by “individuals” who do their best to appropriate the return from their knowledge and whose effort is non-contractible. The organization of the industry into firms is identified to a partition of the set of individuals. In this context, we prove that an organization in which each individual hold his own firms is both stable with respect to unilateral deviation and optimal in the line of the property right approach. If the returns are high enough, this structure is even the only one which shares both properties. Copyright Springer 2007

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[eng] This paper is devoted to the study of the price formation in a context of general equilibrium. In fact, I try to understand how the works on imperfect competition improve this field. This is why I progressively review the contributions of the standard monopoly theory, of the monopolistic competition approach and of the standard general equilibrium theory. Several models are presented in this paper in which I progressively increase the degree of rationality of price maker by moving from a subjective to an objective perception of the demand. In each case, I also briefly discuss the existence conditions. [fre] L'objectif de ce travail est de s'intéresser à la formation stratégique des prix dans un contexte d'équilibre général et de comprendre dans quelle mesure les travaux sur la concurrence imparfaite ont contribué à faire progresser la recherche sur ce thème. Cela m'amènera à passer en revue les apports de la théorie du monopole, des modélisations de la concurrence monopolistique et enfin de la théorie de l'équilibre général. Ces différentes approches me permettront de présenter plusieurs modélisations d'un équilibre général de concurrence monopolistique reposant sur des hypothèses alternatives quant au degré de rationalité des anticipations de demande des monopoles. Dans chaque cas, j'évoquerai également les problèmes posés par la modélisation et je discuterai des conditions d'existence de ces équilibres.