But what does it mean, and what will happen between now and June 8?
What is the dissolution of Parliament?
By law, Parliament is dissolved 25 working days before a General Election.
So from now until the results of the election on June 8 the House of Commons becomes vacant.
This means there are no MPs until a new Parliament is elected.
Theresa May visited the Queen at Buckingham Palace to formally mark the dissolving of Parliament.
Historically, a prime minister had to ask the monarch to dissolve Parliament.
But the 2011 Fixed-Term Parliaments Act made the process automatic.
However, the new act still requires the prime minister to seek the Queen's permission.
Mrs May was driven the short distance from 10 Downing Street to the Palace for an audience with the Queen.
Is the prime minister still in power?
Yes, Theresa May retains all her normal duties and powers until the formation of a new Parliament.
What about MPs?
They revert to being members of the public and lose all their parliamentary privileges.
They are barred from using the title MP - including on websites and Twitter handles.
They are allowed access to Parliament for just a few days in which to remove papers from their offices.
But facilities provided by the House of Commons are no longer available to them from 5pm on the day of dissolution.
What happens to the Government?
Parliament and Government are two separate institutions so the Government does not resign when Parliament dissolves.
Government ministers remain in charge of their departments until the result of the election is known and a new administration is formed.
When will we have a new Parliament?
Successful candidates in the June 8 election are declared MPs immediately after the votes are counted.
They will take their seats at Westminster from June 19 at the next State Opening of Parliament which is summoned by the Queen.