This evaluation study supports the evaluation of Directive 2001/42/EC on the assessment of the effects of certain public plans and programmes on the environment (SEA Directive) as part of the European Commission's Regulatory Fitness Check and Performance (REFIT) programme. This assessment is based on five evaluation criteria: effectiveness, efficiency, relevance, coherence and EU added value. The study found that the SEA Directive brings considerable benefits to the EU, contributing to wider goals on sustainable development and environmental protection through integration of environmental concerns into the appropriate plans and programmes. The study however raised some issues of concern limiting the Directive’s potential to achieve its objectives in an efficient way: uncertainties about the scope of application and the risk of ensuing legal challenges; the challenges in the application of the Directive to strategic planning addressing global and longer term sustainability challenges; the necessity for a flexible application of the SEA procedure and a more efficient practice, in particular in the drafting of environmental reports. The study also identified a few priority issues that should be considered for further action: the clarification of the scope of application of the Directive, a more strategic approach to scoping and the dissemination of good practices.