To become law, the Nice Treaty must be ratified by all 15 EU member-states. EU leaders have committed themselves to ratify the treaty before the end of 2002 and most member-states expect to complete the process much earlier.
If Irish voters reject the treaty in tomorrow's referendum and, as is expected, all other 14 member-states ratify it, the Government can seek to renegotiate it. The only precedent is the case of Denmark, which initially rejected the Maastricht Treaty in a referendum.
Denmark did not succeed in changing the treaty but received clarification of some opt-outs available to it and, the second time around, Danish voters said Yes.
If the Government succeeds in renegotiating the Nice Treaty or securing special provisions for Ireland, it could propose a second referendum. If that referendum was to result in a second rejection, the treaty would fall.
Although the primary purpose of the treaty is to prepare the EU for enlargement, most legal opinion suggests that the EU could accept new members without it. But the institutional changes agreed at Nice are seen as so crucial to allowing a larger EU to function that our 14 partners are likely to seek a way of proceeding without Ireland.
This is such uncharted territory that it is difficult to envisage what form such an arrangement would take. But some experts have suggested that it would mean that Ireland would enjoy an associate status with the EU that would fall short of full membership.
None of this would be possible without Ireland's approval because the rules governing enhanced co-operation at present demand that any such move has the unanimous support of all member-states.
The reality of EU negotiations is that the most difficult issues are resolved by political means rather than by resorting to legal sanctions. In the event of an Irish rejection of the Nice Treaty, it would be in the interest of both the Government and the EU to find a political solution.
If such a solution proves impossible to secure, the most likely outcome of a final rejection of the Nice Treaty would appear to be the end of the treaty and an indefinite delay to the process of enlargement.