Millions of people will have their say on who they want to run the country on General Election day on Thursday.
Polling stations opened at 7am and they will close at 10pm in 645 different constituencies around the UK.
Many people have already sent their votes as a record six million people are voting by post this year.
Even though voting starts early, the first results won't come through until late on Thursday, so we won't know who's won until Friday morning.
Parties have been out and about on the election trail for the last 30 days, trying to convince people to vote for them.
At the last election in 2001, only 59% of adults voted, so experts will be on the lookout to see if this goes up or down.
Polling stations - where people go to vote - have been set up around the country. Many of them are in schools or village halls.
But some are in very unusual places - like caravans, pubs and even a bedroom.
Labour leader Tony Blair, Conservatives leader Michael Howard and Liberal Democrat leader Charles Kennedy have already cast their votes.
A total of 646 seats were up for grabs, but voting has been postponed in one constituency - Staffordshire South - because one of the candidates died.