Green budget tagging can be a useful tool in an overall approach to green budgeting. This introductory guidance was developed by the OECD under the Paris Collaborative on Green Budgeting in collaboration with institutional partners working under Helsinki Principle 4 of the Coalition of Finance Ministers for Climate Action (IADB, IMF, UNDP, World Bank) and draws lessons from existing country practices. It was informed by a series of round-table events with countries implementing green budget tagging. The document aims to provide high-level guidance in relation to designing, implementing and improving green budget tagging.