This paper presents tagging methodologies for 22 environmental domains in the OECD Policy INstruments for the Environment (PINE) database, including seven domains on environmental protection (air pollution, water pollution, soil pollution, solid waste, ozone layer, noise and radiation), six domains on natural resource management (fisheries, forests, freshwater, renewable energy, fossil fuels and minerals) and nine cross-cutting domains (climate change mitigation, climate change adaptation, land degradation, biodiversity, ocean, chemicals management, energy efficiency, circular economy and mercury). The environmental domains in the PINE database support tracking progress towards domestic and international environmental objectives. Tagging environmental domains allows harmonised comparisons across countries, years and policy instrument types.