The article examines the role of social and professional experiences undertaken by young adults in order to construct their Professional Identity. More particularly, two determining dimensions in this identity construction are studied. The first one concerns socialization for work which corresponds to social experience undergone in the family and in education from childhood. The second one concerns socialization by work which corresponds to professional experience undergone by young adults. The latter dimension is studied from a perspective which comprises two methods: direct integration and assisted integration in the world of work. This article ends by pinpointing the most significant characteristics of the contexts and experiences undergone by young adults in the construction of their Professional Identity, and by discussing what measures might be useful to accompany the school to work transition.