The Accession Treaty of Spain to the European Communities is a treaty for the accession of Spain to the European Economic Community —now the European Union— and was signed on June 12, 1985, in the Salón de Columnas of the Royal Palace of Madrid to enter into effect on January 1, 1986. This incorporation was carried out at the same time as that of Portugal. Following this accession, Spain experienced a period of economic prosperity; during five consecutive years, it achieved the highest growth rate of the entire Community.[1] This constituted the completion of liberalization in Spain, opening and rationalization of the Spanish economy after the National Economic Stabilization Plan in 1959.[2] In addition to economic progress, this accession meant the end of the international isolation experienced since the Potsdam Declaration of August 1945, and the stabilization of the recently established democracy.[3]