Spanish European Constitution referendum, 2005

A referendum on the treaty establishing a Constitution for Europe was held in Spain on 20 February 2005. The consultative referendum on ratification of the proposed Constitution of the European Union was approved by 81.8% of voters, although turnout was just 41.8%, the lowest since the end of the Franco era.

The referendum was not legally binding on the government, but paved the way for parliamentary ratification of the constitutional treaty, which happened in the Congress of Deputies on 28 April 2005, with a result of 319 "Yes" to 19 "No", and in the Upper Chamber on 18 May 2005 with a result of 225 "Yes" to 6 "No" and one abstention.

Both the governing Spanish Socialist Workers' Party (PSOE) and the main opposition People's Party (PP) campaigned for a "Yes" vote. They were joined by the Basque Nationalist Party (EAJ–PNV) and the Catalan nationalist Convergence and Union (CiU). Among the parties campaigning for a "No" vote were United Left (IU), the Bloque Nacionalista Galego (BNG, Galician National Block), Republican Left of Catalonia (ERC), Initiative for Catalonia Greens (ICV), the social democratic Aragonese Council (CHA), the Basque nationalist social democratic Eusko Alkartasuna, and the Trade Unions Confederación Intersindical Galega (CIG) and CGT.

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