Martin Dougan
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Why women and poor men couldn't vote in the past

7 May 2015 Last updated at 07:07 BST

More than 40 million adults are expected to vote in the UK general election to decide who runs the country.

But did you know there was a time when women, poor people and many others weren't allowed to have their say?

It took a long time for the right to vote to be opened up to most adults.

Martin's been finding out why being able to have a say is so important.