This practice note explains how the EU Emissions Trading System (EU ETS) was implemented in the UK, including by the Greenhouse Gas Emissions Trading System Regulations 2012 (SI 2012/3038). Following the end of the post-Brexit transition period on 31 December 2020 and the final deadlines for surrender of allowances on 30 April 2021, the EU ETS no longer applies in the UK (save for installations in Northern Ireland that generate electricity for the single wholesale electricity market in Ireland and Northern Ireland).