Does gaining one nationality mean losing another? Few doubts are more common than this, and we know this from experience. At the swearing in of the Constitution, a key formality for acquiring Spanish nationality, many applicants are confronted with this question: are they about to lose their nationality of origin?

The truth is that the answer is much more complex than a simple yes or no answer. If we generalise, we could say yes, that the regulations in force in Spain require, as a prerequisite for acquiring Spanish nationality, the renunciation of the nationality of the foreign country. But the reality is not so clear-cut. Moreover, there are special cases: the dual nationality agreements that Spain has with other countries and which allow applicants not to renounce either of their citizenships.

This is also the case when applying for citizenship by option, carta de naturaleza, or recovery of Spanish nationality.

The general rule: Declaration of renunciation

As explained above, Spanish law requires the renunciation of foreign nationality at the time of acquisition of Spanish nationality (when there are no dual nationality agreements). But this is a mere formality.

The Resolution of the DGRN (Dirección General de los Registros y del Notariado) of 24 May 1993 explains it as follows:

"On the other hand, it is irrelevant that the renouncement of Moroccan nationality by the applicant does not entail the loss of this nationality. As already anticipated by the doctrine of this Centre (Res. DGRN of 24 September 1971), the acquisition of Spanish nationality for those entitled to it could not be subordinated to the circumstance that for the foreign law in question the renunciation of this nationality was not effective. This solution, whereby the renunciation of foreign nationality is no more than a formal requirement, is undoubtedly the one adopted by the current wording of the Civil Code, which only requires that the person <declare> that he/she renounces his/her former nationality (Art. 23.b) CC)".

In other words: once Spanish nationality is granted, Spanish law is indifferent to how the other country in question deals with its citizen. Thus, it is very likely that cases of dual (or multiple) nationality may arise, even if they are not covered by the dual nationality agreements that Spain has signed with various countries.

Therefore, in these cases, much more important than analysing Spanish legislation, it is necessary to study the rules of the country from which the applicant in question comes. It will be this legal system that will decide on the possibility of real loss, or not, of their own nationality as a consequence of this renunciation made to the authorities of another country.

See: How to Acquire Spanish Citizenship By Choice?

The US and UK cases

Let us look, for example, at the case of two of the most important countries in the world:

• The US establishes four cases in which US citizenship can be lost. One of them is applying for citizenship in a second state after the age of 18, but it must contain "an intention to lose US citizenship". While the rules state that applying for citizenship in a third state may constitute grounds for loss of US citizenship, they also establish a presumption of "no intention" to lose citizenship when acquiring another citizenship. And if that "intent" is not clear to the US government, consular authorities must ask the person in question whether he or she wishes to lose US citizenship. If the answer is that "he or she does not wish to lose US citizenship", he or she will not lose it.
• The United Kingdom has a different legislation. The UK allows its citizens to have a second citizenship without losing their UK citizenship. Thus, despite this "mere declaration", it is possible for a British citizen to maintain his or her nationality and acquire Spanish nationality.

Dual nationality agreements

Then, as asterisks to its general legislation, Spain has dual nationality agreements with the Ibero-American countries, and with some of those with a Hispanic colonial past, Equatorial Guinea, the Philippines, and with others with which it shares a border, such as Andorra and Portugal. Nationals of these countries can enjoy dual nationality without any problem.

See: Agreement on dual nationality signed by Spain and France

On the other hand, there is also an agreement to simplify the Spanish nationality procedure for Guatemalan nationals, but this was undermined by a protocol that established that one must have permanent residence in Spain in order to apply for Spanish nationality.

In any case, as we have seen, the existence of dual nationality agreements between Spain and the country in question is not a sine qua non condition for being able to hold two passports simultaneously. Rather, it is the regulations of the country of origin that will decide everything. It will be necessary to assess whether the acquisition of another nationality is considered in that country as a renunciation of that State's nationality, or whether, on the contrary, this "mere declaration" is just that, a dead letter, as is the case in the United Kingdom.