The dust has not yet settled after the referendum on Britain's relationship with the EU, which took place on 23 June 2016. UK voted to leave the EU by 51.9% to 48.1%, which is a winning margin of almost 1.3 million votes. However, it is not yet clear what ‘Brexit’ means or how it will come about – legally and constitutionally. This article seeks to answer the latter question from the standpoint of UK and EU law. The discussion begins with the domestic process before beginning the initial withdrawal negotiations, which is governed by UK constitutional law. The focus then shifts to the process of withdrawing from the EU, which is set out in Article 50 TEU. This article further examines whether ‘Brexit’ can be stopped once Article 50 has been triggered. The penultimate section of the article looks at the legal nature and substantive content of the agreements that might be concluded between the UK and the EU if ‘Brexit’ were to become a reality. The final section of the article examines the UK rules on ratification of such international agreements.