The question of trust is crucial in the field of health. First, because health is indicative of particularly strong issues at the societal, regulatory, institutional or individual levels; secondly, because the boundaries between specialized information validated by legitimate instances and uncommitted information have become permeable; finally, because it appears to be central within relations between actors in the field. In this book, we propose to address the trust in terms of the information and communication phenomena that are at work in the health sector, and to look at the process of building the legitimacy of information in the health sector. health.