The term 'Article 50' has been thrown around a lot in the aftermath of the EU referendum result, so how does it work?
Article 50 forms part of the Lisbon Treaty which was signed by all members of the European Union in December 2007, and it sets out the rules for the process of a member state leaving the European Union.
To activate Article 50, Britain would need to formally notify the European Union that it is leaving - the Prime Minister would do this.
It starts a two-year negotiation period within which Britain should negotiate both its terms of withdrawal from the Union, and the terms of its continuing relationship with the EU and the remaining 27 member states.
Discussions would include things like trade tariffs and freedom of movement between Britain and the remaining member states.
All negotiations must take place without British representatives present, and be agreed with a 'qualified majority' from the remaining states, so the ball is very much in their court as to how negotiations turn out.
If the two-year period ends and Britain has not settled trade agreements, we would end up with default World Trade Organisation tariffs which are higher than those we have currently.