What is it? Article 50 of the Lisbon treaty outlines exactly how an EU member can voluntarily leave the 28-nation bloc. “Any member state may decide to withdraw from the union in accordance with its own constitutional requirements,” the article says.

Why are we talking about it now? Britain recently shocked the world when it voted in a referendum to leave the EU after more than 40 years. But before it can do so, the British government has to officially invoke Article 50 and begin a long and complicated negotiation process to decide on the precise terms of an exit deal and its future relationship with the EU. This would include things like trade tariffs and the freedom of movement between Britain and the remaining states. If no agreement has been reached within two years, Britain would be forced out with no provisions in place, unless, that is, the remaining EU members unanimously agree to extend the talks.

When will Article 50 be enacted? The British government said it needs time to fully prepare for the crucial negotiation period, and is therefore in no hurry to pull the trigger and get proceedings started. This position will likely get harder to hold as pressure mounts from pro-exit groups within Britain that are itching to go it alone, and from EU leaders that are angry with Britain for deciding to leave and are worried that dragging out the process will lead to further damaging uncertainty.