After a short introduction of the IUCN Commission on Ecosystem Management (CEM), the present presentation develops the application of the ecosystem approach by the military sector, in particular in relation to peace-support operations and reconstruction programmes. It describes a simple model of 4 steps. The first step deals with the physical system (“the ecosystem”), the second step with the use of the ecosystem and the third step with its management (institutions and regulations). The fourth step guides the military in taking decisions what (not) to do given the information from steps 1, 2 and 3.