This Practice Note provides the background to the Euratom Treaty and the the UK’s exit from the Euratom Community as a corollary of Brexit. It includes discussion of Brexit and nuclear research and investment, Brexit and nuclear health and safety standards, Brexit and supply of nuclear fuel, Brexit and nuclear safeguards, Brexit and the nuclear common market, and Brexit and nuclear international agreements. It also discusses the Nuclear Safeguards Act 2018 (NSA 2018), the Nuclear Safeguards Regulations, and the key aspects of the Nuclear Co-operation Agreement (NCA) between the UK and Euratom.