The UK is divided into 650 areas called constituencies. During an election everyone eligible to cast a vote in a constituency selects one candidate to be their MP. The candidate who gets the most votes becomes the MP for that area until the next election.
At a general election, all constituencies become vacant and a Member of Parliament is elected for each from a list of candidates standing for election. General elections happen every five years.
If an MP dies or retires, a by-election is held in that constituency to find a new MP for that area.
Most MPs are members of one of the three main political parties in the UK - Labour, Conservative and Liberal Democrat. Other MPs represent smaller parties or are independent of a political party.
To become an MP representing a main political party a candidate must be authorised to do so by the party's nominating officer. They must then win the most votes in the constituency.
UK-wide representation and devolved Parliaments and Assemblies
The UK Parliament has MPs from areas across England, Scotland, Wales and Northern Ireland. In addition, there is a Parliament in Scotland, a National Assembly in Wales and a National Assembly in Northern Ireland.
Separate elections are held for these devolved political bodies (which have been granted powers on a regional level that the UK Parliament was formerly responsible for) - candidates who win seats in these elections do not become MPs in the UK Parliament.