Ecological engineering was defined several decades ago, both in the academic field and in management. I next propose a definition of ecological engineering, in accordance with the two reasons for its French re-emergence, i.e. the prevalence of the concept of sustainable development and the development of applied ecological sub-disciplines. This leads us to suggest that ecological engineering should be ecological in the broad sense, and not only targeted to the ecosystem level. I end the paper by discussing some problems and characteristics of ecological engineering that stem from this definition.