UK voters are going to the polls for the third general election in less than five years.
Polling stations in 650 constituencies across England, Scotland, Wales, and Northern Ireland opened at 07:00 GMT.
After the polls close at 22:00 GMT, counting will begin straight away. Most results are due to be announced in the early hours of December 13.
A total of 650 lawmakers will be chosen under the first-past-the-post system used for general elections, in which the candidate who secures the most votes in each individual constituency is elected.
In 2017, Newcastle Central was the first constituency to declare, announcing its result about an hour after polls closed.
Elections in the UK traditionally take place every four or five years. However, in October, lawmakers voted for the second snap poll in as many years. It is the first winter election since 1974 and the first to take place in December since 1923.
Anyone aged 18 or over is eligible to vote, as long as they are a British citizen or qualifying citizen of the Commonwealth or Republic of Ireland and have registered to vote. Registration closed on November 26.
People do not need a polling card to be able to vote but will need to give their name and address at their local polling station. People can only vote for one candidate or their ballot paper will not be counted.
PM Boris Johnson has cast his vote – he visited a polling station in central London, taking his dog, Dilyn, along with him, and Labor leader Jeremy Corbyn voted in north London.
Brexit Party leader Nigel Farage has used a postal vote.
Many people have already put a cross next to the name of their favored candidate by voting by post – more than seven million people used a postal vote two years ago.