The present thesis develops the effects resulting from the social classifications concerning a certain youth: this is particularly advanced by studying the conditions of access to job by young people and by the confrontation of these results to the theory of the "professional transition" (J. Rose). The classification are analyzed as a necessary condition for the setting up of employment policies and particularly the measures called TUC-CES (collective usefulness jobs - solidarity employment contracts) on one hand, the TUC-CES people are fundamentally analyzed from the point of view and the mobilization strategies developed by institutions which appeal to these young people. On the other hand, this population (TUC-CES people) is analyzing by questioning the steps taken by young people: here, institutional determinations are strongly tied up with individual processes. The concepts of socialization and identity allow the construction of a framework which examines an original program of employment policy.