The polls are split 50/50, but bookies are putting the odds of Britain remaining part of the European Union at £1.30, while the odds of it turning its back on the EU is at £3.40.
There has been so much talk of what fallout there could be from this vote, and voting booths open in a matter of hours.
What will the economic impact of a Brexit be? What about if they remain?
Swati Dhingra from the London School of Economics spoke to Paul Henry.