In environmental governance, the European Union draws on norms of effectiveness, decentralisation, and participation to ensure that its policies and regulations are considered legitimate. This article analyses how the construction of legitimacy in European nature policy has changed over time. Although the norms of participation and decentralisation are increasingly evoked to address the needs of stakeholders and member states in the implementation and financing of Natura 2000, the norm of effectiveness continues to dominate the construction of legitimacy. Effectiveness first acquired its meaning in the context of a science-based approach to Natura 2000 to emphasise the importance of achieving its conservation objectives. More recently, it has become increasingly re-articulated as cost-effectiveness, which reflects a growing influence of neoliberal discourse. The article concludes by discussing the implications of the findings for the legitimacy of European environmental governance.