The international congress “Ecological Engineering: From Concepts to Applications (EECA)” was held from 2 to 4 December 2009, at the Cité Internationale Universitaire de Paris, France. Six keynote presentations and over 60 talks and 40 posters were presented during the 3-day conference. More than 200 participants attended the conference (Fig. 1; Table 1), which was devoted to the exploration of new developments in ecological engineering and thoughts on how to build this field based on sound ecological and conceptual foundations. This conference was organized by the Groupe d’Application de l’Ingénierie des Ecosystèmes (GAIE, Ecological Engineering Applications Group). GAIE promotes the development of ecological engineering and is based in the Ile-de-France. The group is comprised of ca. 125 individuals from many institutions in the region and in France, representing several different disciplines, e.g., ecology, environmental science, management science, engineering and social science. Group activities include organizing conferences, symposia, workshops and working groups, discussion meetings, field trips, research and applied projects.