Prime Minister Theresa May has triggered Article 50 which will start the process of Britain quitting the EU within two years.
In the historic statement to MPs, the PM said “there can be no turning back” and Britain will now be quitting to “make our own decisions and our own laws”.
In the address she said: “I choose to believe in Britain and that our best days lie ahead.
“And I do so because I am confident that we have the vision and the plan to use this moment to build a better Britain.”
She added "I want us to be a truly global Britain – the best friend and neighbour to our European partners, but a country that reaches beyond the borders of Europe too.
"A country that goes out into the world to build relationships with old friends and new allies alike."
European leaders warned of "a very difficult road" ahead for Britons with no guarantee of a trade deal.
Donald Tusk said in his statement: "We already miss you - thank you and goodbye."