Les Presses Universitaires de France and Frémeaux & Associés offer this philosophical history of ecological thought, analyzed and explained by Grégory Quenet, professor of environmental history at the Université Paris Saclay UVSQ, honorary member of the Institut Universitaire de France and holder of the Laudato Si' Chair at the Collège des Bernardins. Humanity's relationship with nature is the object of immemorial dynamics of conquest and frugality, but the awareness of the fragility of the living world to which humanity belongs, and which accompanies the appearance of ecology as an object of reflection and study, is very recent. Understanding the stakes underlying the approaches to ecology and environmentalism in different cultures and eras allows us to respond to the new paradigms and challenges that the world must now face.