The United Kingdom has activated Article 50 of the Lisbon Treaty to signal the beginning of Brexit,

The process was launched on Wednesday, March 29, as the UK's ambassador to the EU, Sir Tim Barrow, handed over a letter that announced Britain's impending separation from the EU.

Below are three things you should know about Article 50 and its role in Brexit, according to Mic:

1. No one's ever done it before.

Article 50, the five-paragraph clause that allows member nations to exit the European Union, became law as part of the Treaty of Lisbon in 2009, the BBC reported. Before that, there was no official path to leaving the EU. Article 50 has never been tested before, as no nations have left the EU.

2. It won't take effect right away.

The U.K. triggered Article 50 on Wednesday, but that doesn't mean it immediately goes into effect. According to a BBC timeline, EU members will establish negotiation guidelines and then begin face-to-face talks in May or June, working to negotiate trade deals, shared security and other policies between the EU and the U.K.

3. The author of Article 50 never expected it to be used.

Former Italian Premier, Giuliano Amato authored Article 50 of the Treaty of Lisbon — and he told a group gathered in Rome in July that he never actually expected any of the EU's member nations to use it.

"I wrote Article 50, so I know it well," Amato said. "My intention was that it should be a classic safety valve that was there, but never used. It is like having a fire extinguisher that should never have to be used. Instead, the fire happened."

British Prime Minister, Theresa May on Wednesday, described the move as “an historic moment from which there can be no turning back.”