The PATTERN project’s general objective is to improve practitioners’ capacity for decision making on climate and environmental policies, by developing an interactive online platform for the economic appraisal of policies and measures. To reach this general objective, the project will develop an operational integrated economic appraisal approach (WP3 and 4), deliver guidelines to bridge ex-post and ex-ante analyses (WP1), build and demonstrate an effective participatory process to create 5 Theories of Change (WP2), build a European Community of Practice for climate and environmental policymaking (WP6), and create a One-Stop-Shop for all policy and decision makers to access and use the project results easily. PATTERN will thus provide decision-makers, stakeholders, and the public with more realistic and operational ability to systematically assess their policies and their consequences. It will provide a basis for improving (i) methodologies, techniques and models for conducting economic appraisal of climate and environmental policies (ii) the broader policy evaluation framework and practices currently used in European countries and their regions and (iii) tailored analysis and engagement strategies structures for the participation and co-creation with relevant stakeholders and key actors to enhance operational capacities and improve the impact of European policies on climate and environment. Overall, results obtained from in-depth ex-post and ex-ante analysis of the PATTERN’s 5 case studies will bring new evidence on the effectiveness of various types of regulatory strategies, instruments and approaches for climate and environmental policies and insights for the design and evaluation of the implementation of major European policies.