Generally, impact assessments must be seen as a tool that addresses important governance challenges, like informed (or knowledge-based) decision-making, policy integration, strategic management, transparency and stakeholder participation. The growing acceptance of sustainable development as overarching policy goal has recently stimulated much interest in methods and tools that assess the impacts of sustainable development policies. This paper will provide a definition and overview of different impact assessment approaches; describe the integrated impact assessment system developed and applied by the European Commission; and present two case studies of Switzerland and Belgium to show the application to national policy-making.