The Prime Minister David Cameron is asking people to vote on whether the UK should remain a member of the European Union (or EU).
The public vote, which is called a referendum, will happen on Thursday, 23 June 2016.
The European Union is a group of 28 countries in Europe whose governments work together.
It was set up to help make trading between European countries easier, as well as travel and immigration.
EU laws affect many areas of our lives as well - like health and safety rules, and even how many fish we're allowed to catch.
For the last 40 years that the UK's been a member of the EU, there's been a debate about our role within it.
Some feel that being part of this bigger club makes the UK richer and more important.
Others argue that the EU takes power away from the UK. They feel that people who aren't British shouldn't be making laws for this country.