Sometimes the government asks its citizens to help them decide what to do about an important issue. They do this by organising a referendum.
A referendum runs in a similar way to an election but instead of voting for a party you are asked to vote either 'yes' or 'no' to a question.
Referendums are not run very often in the UK. The last referendum was in 1975 when the then government asked its citizens to decide if the UK should stay in what is now known as the European Union.
On the 5th May 2011 a referendum is being held to decide what type of voting system we should have in the UK.
The question that citizens will be asked is:
At present, the UK uses the first-past-the-post system to elect MPs to the House of Commons. Should the Alternative Vote system be used instead?
Learn more about both voting systems here.