As countries implement stricter environmental policies, the need for tools to compare countries’ environmental policy stringency is becoming more pressing. The OECD Environmental Policy Stringency (EPS) index has become a widely used tool for policy analysis since its creation in 2014. This paper updates the EPS index over three decades from 1990 to 2020, across 40 countries and 13 policy instruments, focussing on climate change and air pollution mitigation policies. It up-grades the index structure across all years, adding a new sub-index that measures the strength of technology support policies, which complements the existing structure of market based and non-market based sub-indices. The paper shows evolving developments – across countries and time – in the stringency of environmental policies.