This study uses a multi-agent model to illustrate the behaviour of economic players in a context of rapidly evoIving environmental policy. The area under study is represented by a sector of Reunion island with a high concentration of pig farms (Grand Ilet) in the upland region and extensive sugarcane plantations in the coastal zone. The pollution problems associated with pig rearing are being addressed by the public authorities, which must choose a set of environmental measures suited to the. local context. After illustrating the approach and the results that can be obtained using multi-agent systems model reality, we discuss their advantages for the implementation of decision-making and negotiation tools.