On March 29, 2017 (today) the United Kingdom formally invoked Article 50 of the European Union treaty allowing member nations to withdraw from the largest single market in the world.

The UK and the EU will spend the next two years unraveling four decades of close political and economic co-operation while trying to negotiate a free trade deal.

The decision to withdraw from the EU was the result of a very narrowly won referendum (51.9%) in June of 2016. Support for leaving the EU mainly hinged on a desire for autonomy with regard to immigration and a rejection the authority of the European Court of Justice.

This handout photo was provided by 10 Downing Street. It shows Theresa May signing the four-page hand-written letter to Donald Tusk, President of the EU.

(Photo: JAY ALLEN / NO10 / MOD / HANDOUT, EPA)