Voting is underway in the proposed 30th amendment to the Constitution.
Polls will close at 10pm tonight and an indication of the result will be known by mid-morning tomorrow.
In all, 3.13 million people are eligible to vote in this referendum on the Treaty on Stability, Coordination and Governance in the Economic and Monetary Union.
They all should have received a polling card telling them where to vote, but they do not need it to cast a ballot and voters are encouraged to bring along some form of photo ID.
All voters are encouraged to use their democratic right and go out and vote at the hundreds of polling stations in all 43 constituencies.
At 10pm tonight the ballot boxes will be sealed and transferred to 26 count centres across the country.
Counting gets underway at 9am tomorrow with a good indication of the result expected later in the morning.