Polling is underway for the referendums on same sex marriage and the lowering the age at which citizens are eligible to be President.
Polls opened at 7am, and will stay open to 10pm.
Residents of Carlow and Kilkenny are also electing a new TD to fill the seat left vacant by EU Agriculture commissioner Phil Hogan.
After polling stations close at 10pm tonight, the ballot boxes will be sealed, transported and stored securely before counting gets underway at 9am tomorrow.
Indications of the result are expected by mid-morning, with a final declaration of how the country voted due by about 5pm tomorrow.
Voters can present their polling card to vote, but can vote without it as long as they have valid photo ID such as a passport, driving licence or social welfare card.