A. NATIONALITY BY RESIDENCE
This is, without a doubt, the naturalisation procedure to which most foreigners resort. This form of acquiring nationality requires the residence of the person concerned in Spain for the time and under the conditions legally established. In other words, it is based on physical ties.
B. NATIONALITY BY OPTION
Generally speaking, it is due to the close family ties of the person concerned with Spanish citizens.
Thus, those who are or have been subject to the parental authority of a Spaniard, those whose father or mother was Spanish and born in Spain, and adoptees over the age of eighteen can opt for Spanish nationality.
C. NATIONALITY BY POSSESSION OF STATE
This is a rare way of acquiring nationality based on the fact that the person concerned has possessed and used this nationality for ten years. The requirements are that the person concerned acts in good faith in the possession and use of Spanish nationality and that there is a title of nationality registered in the Civil Registry, even if such title is annulled.
D. NATIONALITY BY LETTER OF NATURE
It is granted at the discretion of the Government by Royal Decree.
In this case, the interested party must prove that exceptional circumstances exist in order for the nationality to be granted. The assessment of the exceptional circumstances alleged is not subject to the general rules of administrative procedure and its assessment is individualised. The exceptional circumstances on which the interested parties base their application are of a very varied nature: cultural, sporting, scientific, solidarity-based, etc.
E. NATIONALITY BY MERE PRESUMPTION
Spain recognises nationality by simple presumption to the children of foreign parents born in Spain in the case that the country/countries of origin of the parents do not attribute a nationality or if both parents do not have a nationality.