Les consommateurs disposent d’une rationalité limitée et sont sujets à divers biais cognitifs. La thèse étudie les conséquences des biais de rationalité sur le comportement des consommateurs ainsi que les implications sur la politique de consommation. Chacun des trois chapitres de la thèse est consacré à un biais particulier (surestimation de la qualité, erreurs d’anticipation de l’utilité, biais de projection) dans un contexte concurrentiel déterminé. Les deux premiers chapitres sont bâtis sur des modèles de duopole standards auxquels sont intégrés des biais de rationalité : le premier est un duopole avec différenciation horizontale inspiré de Dixit (1979), tandis que le second envisage un modèle de différenciation verticale adapté de Gabszewicz & Thisse (1979). Le troisième chapitre étend à trois périodes la modélisation du biais de projection proposée par Loewenstein et al. (2003). J’aboutis à la conclusions que, si les biais cognitifs conduisent dans certains cas à des choix sous-optimaux (chapitres 1 et 2), les consommateurs naïfs peuvent également être avantagés par rapport aux agents sophistiqués (chapitre 3). Ce constat plaide en faveur d’une intervention circonstanciée et mesurée sur le marché. Enfin, des recommandations de politiques économiques sont formulées: je prône une approche renouvelée du droit de la consommation, qui ne serait plus fondé principalement sur l’information du consommateur mais davantage sur des mesures de redressement cognitif. Des exemples de mesures concrètes sont discutés tout au long de la thèse. / Consumers have bounded rationality and exhibit cognitive biases. The thesis studies the consequences of such biases on consumer choice and implications on consumer policy. Each chapter of the thesis investigates one specific bias (quality bias, utility misperception and projection bias) in a given market structure. The first two chapters focus on stan- dard duopoly models, in whichcognitive biases are incorporated: I build a horizontally differentiated duopoly based on Dixit (1979)in chapter 1, and a vertically differentiated duopoly inspired by Gabszewicz & Thisse (1979) in chapter 2. As for the third chapter, it extends to three periods, in a monopolistic framework, the projection bias model proposed by Loewenstein et al. (2003). I come to the conclusion that, while cognitive biases sometimes lead to suboptimal consumption decisions (chapters 1 and 2), naive consumers can be better off than their sophisticated counterparts(chapter 3). This observation pleads in favor of a non-systematic and context dependant legal intervention to counter cognitive errors. I argue in favor of a new approach of consumer policy, that would focus less on information disclosures in favor of debiasing schemes. Examples of such debiasing policies are discussed throughout the thesis.

The requirement to exhibit moderation in the marketing of loans is still new and relatively undefined. According to the preparatory works of the new consumer credit law it is the task of the practitioners of the law to provide the more precise definition of the requirement. In the preparatory works it is also expressed that human tendensies such as overoptimism and time-inconsistent preferences as well as framing effects in the presentation of a loan may be exploited in the marketing of loans. The terms "overoptimism", "time-inconsistent preferences" and "framing effects" can be derived from the behavioral research made on human economic behavior. The mentioning of them in the preparatory works raises the issue of which role behavioral sciences plays, and may come to play, in the interpretation of the moderation requirement. Put in a wider perspective, it also raises the question of which role behavioral sciences may come to play for the practice of marketing law in general.In this essay, the requirement to exhibit moderation in the marketing of loans is first examined and compared to other similar kinds of requirements. Then, the concepts of overoptimism, time-inconsistent preferenses and framing effects are analysed and put into relation to the requirement. In order to determine whether or not there is a need for influences from the behavioral sciences in the practice of marketing law the view of consumers held by the courts and the legislator is then examined. Finally, ways of incorporating a behavioral sciences perspective in the interpretation of the moderation requirement as well as in the practice of marketing law in general are proposed. It is concluded that certain experi-mentally observed psychological effects could serve as guidance in determining whether or not the moderation requirement is respected. It is also concluded that behavioral research can help paint a more realistic of the average consumer in the general practice of marketing law. With regards to the current practice of marketing law, the step to explicitly incorporating a behavioral sciences perspective into it may seem like a big one. The discussion surrounding the practice of what has been called "behavioral law" has, however, only just begun.

The current round table gathers four renowned specialists infields such as Law and Economics, Civil Law, Litigation, and others, inorder to discuss the relevance and impact of the development of behavioral psychology and neuroscience in Law. thus, the guests addressthe criticism directed from the mentioned study fields to the modelof individual rationality that underlies traditional legal institutions. / La presente mesa redonda convoca a cuatro reconocidos especialistas en materias como el Análisis económico del Derecho, Derecho Civil, Derecho Procesal, entre otras, con la finalidad de discutir la relevancia e impacto que tienen los recientes descubrimientos realizados por el desarrollo de la psicología conductual y las neurociencias en el Derecho. De esta forma, los invitados abordan el cuestionamiento que se dirige desde las áreas de estudio referidas hacia el modelo de racionalidad individual que subyace a las instituciones jurídicas clásicas.