Abstract : Having been hard criticized following the mishaps of « new economy », the sell-side analysts, salaried by the brokerage firms, represent necessary and inevitable actors however, both for management of firm and for investors and especially since the evolution of accounting regulation is being supposed to do answer their concerns. This research has as vocation to try to understand how the sell-side analysts achieve their judgment. The first part of this thesis shows how the structuring of the previous researches, according to their apprehension of future, allows to construct a progress in the way the judgment of the analyst is studied by inserting progressively the social inscription of this last. This dimension acts then, as starting point for an understanding and qualitative step, founded on the method of Grounded Theory. The second party offers a model of analysis of the training of judgment as practice institutionally supervised and on a local level adjusted. This research shows how the inscription of the analyst how within its « organizational field » leads to have to take into account thinking-ways and to interact cognitively with other actors. The making of his judgment blends in then on a process of correlation between a qualitative and quantitative modelling, and an analysis in dynamics of Stock Exchange prices. This training of judgement also adjusts according to the degree of relational building in established by the analyst with his customers.