Twenty-eighth Amendment of the Constitution of Ireland

The Twenty-eighth Amendment of the Constitution of Ireland permitted the state to ratify the Lisbon Treaty of the European Union. It was effected by the Twenty-eighth Amendment of the Constitution (Treaty of Lisbon) Act 2009, which was approved by referendum on 2 October 2009 (sometimes known as the Lisbon II referendum).

The amendment was approved by the Irish electorate by 67.1% to 32.9%, on a turnout of 59%. The amendment's enactment followed the failure of a previous attempt which was rejected in the Lisbon I referendum, held in June 2008 (this failed proposal was also intended to be called the "Twenty-eighth Amendment"). The successful referendum in 2009 represented a swing of 20.5% to the "Yes" side, from the result in 2008.

Following the referendum, Dáil Éireann (the lower house of parliament) gave its approval to the Treaty on 8 October 2009. The President of Ireland Mary McAleese signed the amendment of the constitution into law on 15 October. These formalities having been conducted, the state ratified the treaty by depositing the instrument of ratification with the Italian government on 23 October. The Treaty of Lisbon entered into force on 1 December 2009.

A 1987 decision of the Supreme Court established that ratification by Ireland of any significant amendment to the Treaties of the European Union requires an amendment to the Constitution of Ireland. All constitutional amendments require approval by referendum.

A referendum on the Treaty establishing a Constitution for Europe of the European Union was expected to be held in 2005 or 2006 but was cancelled following the rejection of the Constitution by voters in France in May 2005 and in the Netherlands in June 2005. The Treaty of Lisbon represents the European-wide political compromise that was agreed upon in the wake of the rejection of the Constitution. It preserves most of the content of the Constitution, especially the new rules on the functioning of the European Institutions, but gives up any symbolic reference to a Constitution. (See Treaty of Lisbon compared to the European Constitution.)

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