Prime Minister Theresa May will trigger Article 50 on March 29, which formally begins the United Kingdom's exit from the European Union.
What's next: Negotiations over the exit, which can expected to last two years. Departing a single market won't be simple, and May has already said she wants a "hard" Brexit, rather than leaving one foot in the door. At this pace, the U.K. will be fully split from the E.U. by early 2019.