This PhD dissertation deals with the comprehension of the origin of herding behaviors, in financial markets. After a literature review, the development of Scharfstein and Stein's (1990) model enables us to structure several hypotheses on herding behavior, considered as a binary choice: to follow other agents or act as contrarian. Since herding behavior cannot be clearly proved by econometric tests, two alternative empiric approaches are successively envisaged. An exploratory questioning of portfolio managers bring fruitful testimonies on this topic.On the other hand, an experimental design, inspired from Cote and Sanders (1997), allows us to measure the variables at stake. The main contribution of this research is to provide concrete empiric elements on real herding behavior, and its reasons. The two essential factors revealed by these approaches are (1) the importance of the preservation of the manager's reputation and (2) the inverse correlation between herding behaviors and the ability of actors.
