After weeks of debate and bitter battles in Parliament, the Article 50 Bill has cleared its final hurdle tonight.
Theresa May is now a position to inform the European Union we are leaving.
That means Britain faces the most intense, arduous and complex negotiations since the end of the Second World War.
Both the EU and the Government agree on one thing: this is ‘unprecedented’ territory and neither side knows how the talks will pan out.
Here is your guide to what happens next, the key players and the issues which could make or break the negotiations.