In recent decades, political scientists have devoted substantial attention to the changing role of the state towards more inclusion of non-state actors in policymaking. This deliberative turn, or move towards governance, may signal inability to handle complex problems without cooperation with nonstate actors. On the other hand, governance is frequently credited with generating legitimate decision-making processes and results. In some instances, non-governmental actors have even taken the lead in policymaking. One archetype of such private governance, which has received significant scholarly attention, is forest certification. The Forest Stewardship Council (FSC) is frequently described as the most democratic and therefore legitimate forest certification organization since it grants equal voting rights to three stakeholder groups in the formulation of criteria for responsible forestry: environmental non-governmental organizations (ENGOs), social groups (indigenous peoples and labor organizations) and forest owners. However, in Sweden, a country often described as a role model in forest certification, the FSC has increasingly received critique for failing to generate legitimate processes and results, and recently three of five ENGOs have chosen to exit the FSC organization. Such processes of de-legitimation have received little attention in the forest certification literature. This thesis therefore provides a critical assessment of the legitimacy of forest certification in Sweden. Legitimacy is analyzed through concerned stakeholders’ perceptions of both procedural qualities (input legitimacy) and problem-solving capacity (output legitimacy). This study of legitimacy is combined with an assessment of the ability of certification to enhance environmental protection, defined as changes in both forest management practices and biophysical conditions. The thesis focuses not the least on legitimacy on the local level, which is where the actual implementation takes place. Today local studies of the legitimacy of forest certification are rare. Both quantitative and qualitative research methods are applied and a number of sources are analyzed: forest monitoring data, survey data, interviews with and documents produced by the participating stakeholders. Papers I and IV analyze the perceived legitimacy of forest certification, while Papers II and III analyze forest certification schemes’ ability to enhance environmental protection. The results show that a process of de-legitimation is occurring in Swedish forest certification. In particular, certification has lost legitimacy with ENGOs, which increasingly consider Swedish forest certification to lack both input legitimacy and output legitimacy. Moreover, although the Swedish FSC standard pays attention to reindeer husbandry, the results show that reindeer herders consider themselves to have limited power to influence long-term forest planning and management (low output legitimacy). The forest industry, on the other hand, increasingly grants legitimacy to forest certification due to customer demands, which are created not the least by pressures from international ENGOs and by EU regulation. The results also show that Swedish forest companies have paid more attention to their environmental practices after obtaining certification. However, to what extent these changes result in positive environmental impacts remains uncertain, especially since forests in Sweden grow slowly, which requires analyses over time. There are also measurement problems resulting from the low certification rate among small-scale forest owners and from the fact that certified small-scale owners tend to be more active in their management. These findings highlight that research on private forest governance should not neglect the role of the state, neither as a buyer nor as a regulator. These findings also suggest that further research should pay attention to power asymmetries in private governance and develop methods for better understanding and evaluating the certification schemes’ environmental and social impacts.