One speaks about double dividend when the revenue neutral substitution of environmental taxes for other taxes leads to both an environmental benefit and an economic one. The first theoretical studies of this question, in a general equilibrium framework, argue that there is no secondary benefit in the sense of a reduction in tax distorsions. However, there are cases in which positive welfare gains can be obtained : when the environmental tax reform involves a tax shirting from labor to other factors or when there are feedbacks effects from environmental quality to the economic system. When studying this issue under the assumptions of imperfect competition and non clearing labour market, the occurrence of a double dividend becomes more likely...