People are taking to Twitter to share the reasons why they're voting today.
It's the battle for London mayor and fight for control of the Scottish parliament, as well as council elections across England, Welsh Assembly and Northern Ireland Assembly.
And if you're wondering whether you can really be bothered to head to your local polling station and cast your vote, these reasons might change your mind.
1. Because the right to vote was a hard won struggle.
-- Andrew Copson (@andrewcopson) May 5, 2016
#PollingDay Don't forget to get to the polls and vote! People fought long and hard for democracy, don't waste it!
-- Kasi (@KasiTheProphecy) May 5, 2016
Unless you are a land-owning male over 30 someone had to fight for you to get the vote - go use it #PollingDay
-- Lizzy Parker (@parkerpannell) May 5, 2016
2. Particularly for women.
-- Louise (@RedLiverbirdLou) May 5, 2016
When I was little my mum told me about an apocryphal suffragette relative so I would always vote. Take your daughters to vote. #PollingDay
-- Ruth Hunt (@ruth_hunt) May 5, 2016
-- Yasmin Khan (@ykhan100) May 5, 2016
3. Your vote actually does make a difference.
Conservatives got a UK majority because of 900 people voting. So I'm not buying the "My vote doesnt make a difference" crap. #PollingDay
-- Jake Burdis ? (@jakeburdis) May 5, 2016
4. Not every country around the world has a free, fair voting system like we do.
Our ability to participate in democratic elections is something many envy and has been a hard won right for many - use it on #PollingDay
-- Paul Duxbury (@PaulDuxbury) May 5, 2016
Don't forget to vote folks, we are lucky to live in a country that allows us to do so. #PollingDay
-- Ollie (@kyuri1985) May 5, 2016
People who lived under brutal regimes know that voting is not a luxury #PollingDay
-- mellow mo (@calderax50) May 5, 2016
5. Because otherwise you can't really complain about those in power.
-- James Melville (@JamesMelville) May 5, 2016
6. Because a minority shouldn't be able to decide.
In the local elections in 2012 overall turnout was less than a third (31.0%). Don't let the minority decide who wins. Vote today #PollingDay
-- Jack Slater (@Jack_Slater) May 5, 2016
7. To stop someone you really don't want as London Mayor.
I wasn't massively interested in #pollingday until Goldsmith's abhorrent campaign. Props to him for getting people motivated to vote ?
-- Holly Brockwell (@holly) May 5, 2016
8. or if you particularly want (or don't want) to see this happen.
If Sadiq Khan wins London, I will run naked down Regent Street with a sausage up my bum in protest #LondonMayor2016
-- Katie Hopkins (@KTHopkins) May 4, 2016
9. Because it's a lovely day anyway, so you may as well.
-- Andrea Sutcliffe (@Crouchendtiger7) May 5, 2016
-- Sophie Earnshaw (@sophisabella) May 5, 2016
10. And it really doesn't take very long.
-- Cat Johnson (@katjohnsonmeow) May 5, 2016
11. And then you can take a nice selfie for your followers and encourage them to vote too.
-- Kay - ??? (@inheadkay) May 5, 2016
12. And there might be a touch of comedy along the way.