The treaty made simple
The Lisbon Treaty is a complex legal document and its fate will be decided today by voters in this country.
The campaigning and debating is all over, so now it's up to the people to make their decision.
What effect will the Treaty have on tax?
Lisbon continues the veto allowing a state to block changes on taxation. But it also contains a provision allowing the European Council, if it secured the support of all member nations, to change the rules in favour of majority voting.
Ireland's independent Referendum Commission said in effect the veto on tax remains in the Lisbon Treaty, again at the European Council level and thirdly in the national parliament.
What does the treaty do on the military front?
Over the last five decades Ireland has built an internationally respected reputation for UN peacekeeping, thanks in part to neutrality.
Fears have been expressed over military expansion in Europe and demands on countries to massively increase their defence budgets.
Under the Lisbon Treaty, foreign, security and defence decisions must be made unanimously.
Ireland's neutrality is protected but there is an obligation to aid and assist, in accordance with the UN, a state which is the victim of armed aggression.
The type of aid and assistance that is required is not specified, but it must not affect security and defence policies of states, including Ireland's neutrality.
Also, states are obliged to help each other after a terrorist attack, natural or man-made disaster.
What happens to Ireland's European Commissioner?
With 27 states in the enlarged EU, and if the treaty is passed, only two-thirds of the Union will nominate a commissioner in 2014, creating 18 posts. Currently, each state has a commissioner.
The right to nominate a commissioner will rotate among states, with countries putting forward a name for two out of every three commissions, or 10 years out of every 15.
Precise details on how this will work have not yet been decided.
How are Ireland's voting powers affected?
Under Lisbon, from 2014, voting rules change to a qualified majority or double majority.
It means decisions must meet two conditions -- first, 55pc of states must agree, and second, supporting states must represent 65pc of the EU's 500 million citizens.
What's the story with "qualified majority voting"?
At present, it applies to a wide range of issues, including agriculture, competition rules, consumer protection, environment and judicial cooperation in civil matters.
Lisbon proposes to apply it to energy, asylum, immigration, judicial cooperation in criminal matters, and sport.
At least four countries must be opposed to a decision in order for it to be blocked, but if fewer than four join forces, then the qualified majority will be deemed to have been reached, even if the population target is not.
How will the European Council change?
Under Lisbon, a new post of president will be created and elected by qualified majority by the council to chair and coordinate its work. Terms run for two-and-a-half years and nominees can hold the office twice.