The Treaty of Accession 1985 was the agreement between the member states of the European Communities, Spain and Portugal, concerning these countries' accession into the EC. It entered into force on 1 January 1986. The Treaty arranged accession of Spain and Portugal to the EC and amended earlier treaties of the European Communities. As such it is an integral part of the constitutional basis of the European Union.^[1]

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Treaty concerning the accession of the Kingdom of Spain and the Portuguese Republic to the European Economic Community and to the European Atomic Energy Community

Treaty of Accession 1985 Treaty between the Kingdom of Belgium, the Kingdom of Denmark, the Federal Republic of Germany, the Hellenic Republic, the French Republic, Ireland, the Italian Republic, the Grand Duchy of Luxembourg, the Kingdom of the Netherlands, the United Kingdom of Great Britain and Northern Ireland (Member States of the European Communities) and the Kingdom of Spain, the Portuguese Republic, concerning the accession of the Kingdom of Spain and the Portuguese Republic to the European Economic Community and to the European Atomic Energy Community.
Countries involved in the treaty, with newly joining countries in yellow and existing EU countries in blue.
Signed	12 June 1985
Location	Madrid, Spain Lisbon, Portugal
Effective	1 January 1986
Condition	Ratification by Spain and Portugal and all 10 Member States of the European Communities
Signatories	European Union (10 members)  Spain  Portugal
Ratifiers	12 / 12
Depositary	Government of the Italian Republic
Languages	All 8 official Languages of the European Communities, Spanish and Portuguese

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The full official name of the treaty is:

Treaty between the Kingdom of Belgium, the Kingdom of Denmark, the Federal Republic of Germany, the Hellenic Republic, the French Republic, Ireland, the Italian Republic, the Grand Duchy of Luxembourg, the Kingdom of the Netherlands, the United Kingdom of Great Britain and Northern Ireland (Member States of the European Communities) and the Kingdom of Spain, the Portuguese Republic, concerning the accession of the Kingdom of Spain and the Portuguese Republic to the European Economic Community and to the European Atomic Energy Community.

• 1986 enlargement of the European Communities
• Enlargement of the European Union