Voluntary multi-stakeholder instruments such as certification schemes have played an increasing role in global environmental governance. Implemented for nearly two decades, the Forest Stewardship Council is emblematic of these new forms of private environmental governance based on market values. It has emerged as one of the most promising solutions to global forest concerns. Although there have been many studies on the impacts of FSC, this remains a controversial and contested issue. Drawing on a critical review of the methodologies used to date to assess the impacts of forest certification schemes, this paper identifies three challenges that evaluation scholars have to address in order to assess the FSC scheme in terms of environmental effectiveness: developing a point of reference to which certification measures must be compared; extending and contextualising the scope of the evaluation; and analysing all effective management measures that contribute to obtaining the environmental result observed before examining the specific role of certification. The paper then shows why the concern-focused evaluation framework appears to offer some interesting perspectives for addressing these challenges. (Texte intégral)