International audienceThis article is related to the nature of social ties remained between student graduates become engineers: are they just the proof of an Alumni solidarity between graduates of the same school ? or the survival of their students sociability ? or, the consequence of specialized professional environments in which multiple opportunities to meet same graduates maintain the collective sense of belonging to a group of alumni. Following trajectories of relationships, this study illustrates that these links rather explained by the last two logical (friendship and frequent professional contacts) than by the existence of a "esprit de corps", describing the great French Schools.Sur la base d'entretiens réalisés avec des diplômés d'...