Obtaining Spanish nationality is a straightforward process, as applicants are not required to undertake any citizenship tests, like the United States' English and civics test. However, because of Spain's special relations with a number of countries around the world as a former global power, the requirements for applicants of certain nationalities, concerning mainly the duration of lawful residency in Spain, vary greatly. Therefore, the main task before pledging allegiance to the Spanish flag is not the naturalization process itself, but determining whether you are legally eligible to apply in the first place.
Determine whether you are eligible of becoming a Spanish national immediately by option. Eligible applicants are children of Spanish nationals and born in Span, as well as people under the guardianship of a Spanish national. All other cases of nationality by option (parentage determination and adoption during adulthood) require applicants to reside lawfully in the country for two years.
Reside in the country continuously for at least 10 years. The period of residence is reduced to five years if you are a refugee seeker, two years for nationals of Latin American countries, Andorra, Philippines, Equatorial Guinea, Portugal or people of Sephardic origin and one year for special cases, as defined by the Spanish Ministry of Justice. The period of residence is verified with a "empadronamiento," proving your registration with your local authorities.
Complete the "SOLICITUD DE NACIONALIDAD ESPA'OLA POR RESIDENCIA" application form. Obtain the document from your local civil registration office or download it from the website of the Spanish Ministry of Justice.
Accompany the application with your passport, foreign identity card, registration certificate (empadronamiento), birth certificate (translated if necessary), criminal record from your country of origin (translated) and proof you can support yourself financially (job contract, payroll employment report or other evidence). Consult the Ministry of Justice website for documentation requirements of special cases.
File your application to your local civil registration office, not directly at the Ministry of Justice. Find your local office through the Ministry's online search engine. After your application is accepted, you will be invited to swear loyalty to the King and promise to obey the Spanish Constitution and laws in a formal ceremony, according to the Ministry's instructions.