Should we worry about the erosion of biodiversity? What can be done? Several studies carried out within the joint research unit LAMETA present biodiversity as a rather complex notion, the value of which does not accurately appear on any market. However, the partial assessments that can be made through other means show its importance, but its preservation is no easy thing. Since biodiversity greatly concerns private properties and also sovereign States for which the protection of the nature is not (yet) a priority, the statutory approaches are of limited help. We must try to gain a better understanding of the social forces that compromise biodiversity and use these same forces to preserve it.