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4 May 2015 Last updated at 16:22 BST
It's a big deal for people across the country, but everyone's watching Scotland in particular.
This is because the election result could have a huge impact on who runs the next UK government.
Jenny went to a youth club in Glasgow to find out more.

The 25-year-old American born striker made 37 appearances and scored seven goals during his 12 months at Tynecastle.
Johnsen also made his first international appearance for Norway while a Hearts player.
The Edinburgh club has strengthened up front, signing Kyle Lafferty during this transfer window.
Johnsen was brought to Hearts by former head coach Robbie Neilson after leaving Bulgarian club Litex Lovech.
And Neilson's successor, Ian Cathro, had to deny reports of an argument with the striker at half-time during a game against St Johnstone in May.
Den Haag, managed by Alfons Groenendijk, the former Manchester City midfielder and former Ajax assistant, finished 11th in the Eredivisie last season.

The Super League side have played at the ground, which is owned by Bank of Ireland, since 1895.
As it stands, their lease will terminate at the end of December.
"The current lease and cost of repairs is crippling the club," Carter told BBC Radio Leeds.
"We made a reasonable offer of what we could afford over the next 18 months but never got a reply and Wednesday was the deadline that we had to give six months' notice.
"The ball is in their court now and it may be that we get no response and they are happy to take back ownership of the ground. I can't talk on their behalf."
The Wildcats were hoping to move to a purpose-built stadium for the start of the 2015 season but work has never started on the project.
Carter says he has spoken to several different clubs about possible groundshares for 2016.
He added: "We've already looked at alternatives because it's no good us saying we have six months to get something sorted - realistically you need to have something in place well before then.
"We've had a number of discussions with other grounds at this time, which will remain confidential."

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1 October 2014 Last updated at 19:45 BST
The Global AgeWatch Index 2014 measures the social and economic welfare of those over 60 in 96 countries.
According to the index, Norway comes on top and the worst country is Afghanistan, followed by Mozambique.
Here's the story - in 15 seconds.
The UK's biggest vote - the general election - takes place on 7 May.
[NEXT_CONCEPT]
Hearts have sold Bjorn Johnsen to Dutch top-rlight club ADO Den Haag for an undisclosed transfer fee.
[NEXT_CONCEPT]
Wakefield Trinity Wildcats chairman Michael Carter says the club could be forced to leave their Belle Vue home after serving notice to the administrators of the ground's lease.
[NEXT_CONCEPT]
A new index suggests that African countries are among the world's worst places to be old in.