Policy Impact Assessments (IAs) are formal, evidence-based procedures that assess the economic, social, and environmental effects of public policy. They have been incorporated into policy making in the OECD countries and the European Commission. Policy Impact Assessments (IAs) are formal, evidence-based procedures that assess the economic, social, and environmental effects of public policy. They have been incorporated into policy making in the OECD countries and the European Commission. Key types of impact assessments include global assessments (global level), policy impact assessment (policy level), strategic environmental assessment (programme and plan level), and environmental impact assessment (project level). Impact assessments can focus on specific themes, such as social impact assessments and gender impact assessments. IAs can improve legislation by: