The paper provides a comparative analysis of the regulatory impact assessment (RIA) systems of the six Western Balkans administrations, showing how they have been used to ensure evidence-based lawmaking and EU law transposition. The regulatory and methodological frameworks, institutional set-ups and arrangements for RIA and EU law harmonisation, including government planning, EU accession negotiations and transposition, have been systematically analysed to identify the strengths and weaknesses of national systems and practice and to share knowledge and good practices. Key policy recommendations have been provided to address major shortcomings and improve the national systems of regulatory policy making.