Citizenship law in Spain is regulated under Article 24 of the Civil Code, together with various International Treaties of Double nationality signed with other countries. Spanish citizenship is in general granted under the principle of ius sanguinis, though the system also contains some elements of ius soli. Thus, citizenship is given at birth to individuals who are born to at least one Spanish parent. Spanish citizenship can also be obtained either by option or by naturalisation. Acquisition of Spanish citizenship by option is given to individuals with special links to Spain who must express their wish by means of a declaration. In terms of naturalisation, citizenship can be obtained after satisfying a residency period of at least ten years.
With regards to dual nationality, the Spanish Civil Code establishes the possibility of dual citizenship in the case of countries with historical links or agreements with Spain. Such applicants are not required to renounce their previous nationality and reciprocally Spanish citizens can keep their citizenship when naturalising in one of those countries. Spanish citizens are also allowed to acquire a second citizenship in a country with no ties to Spain, subject to a declaration that they want to retain the Spanish nationality. Such declaration needs to be made within three years from the acquisition of another citizenship. However, in those cases whereby Spanish citizenship is acquired by a foreigner through naturalisation, the applicant must renounce the previous nationality. In the case of dual citizenship, the Spanish nationality always prevails before the Spanish authorities.