Downing Street has confirmed prime minister Theresa May will trigger Article 50 on Wednesday 29 March, starting the process of the UK leaving the EU.
It is expected to take up to two years to complete the withdrawal, but the road ahead remains unclear, with many anticipating that it could take much longer.
No state has ever left the European Union before, and the rules for exit, contained in Article 50 of the Treaty of Lisbon, are brief.
After Article 50 is triggered, the Treaties that govern membership no longer apply to Britain, and the terms of exit will then be negotiated between Britain's 27 EU counterparts, with each having a veto over the various conditions.
It will also be subject to ratification in national parliaments across the EU.