According to the Peruvian Constitution and nationality

Nationality

Nationality is membership of a nation or sovereign state, usually determined by their citizenship, but sometimes by ethnicity or place of residence, or based on their sense of national identity....

 legislation passed in 1996 as well as an executive order declared in 1997, Peruvian nationality

Nationality

Nationality is membership of a nation or sovereign state, usually determined by their citizenship, but sometimes by ethnicity or place of residence, or based on their sense of national identity....

 can be passed by birth via jus soli

Jus soli

Jus soli , also known as birthright citizenship, is a right by which nationality or citizenship can be recognized to any individual born in the territory of the related state...

 or by registration if born overseas and duly registered at a Peruvian embassy or consulate before the child reaches 18 years of age. In addition, infants or minor children found abandoned on Peruvian territory are assumed to be Peruvian citizens. This is consistent with the nationality law

Nationality law

Nationality law is the branch of law concerned with the questions of nationality and citizenship, and how these statuses are acquired, transmitted, or lost. By custom, a state has the right to determine who its nationals and citizens are. Such determinations are usually made by custom, statutory...

 of most countries of the Americas

Americas

The Americas, or America , are lands in the Western hemisphere, also known as the New World. In English, the plural form the Americas is often used to refer to the landmasses of North America and South America with their associated islands and regions, while the singular form America is primarily...

.

Those children born overseas to Peruvian mothers or fathers who were not registered before reaching 18 years of age can acquire Peruvian nationality

Nationality

Nationality is membership of a nation or sovereign state, usually determined by their citizenship, but sometimes by ethnicity or place of residence, or based on their sense of national identity....

 by choice if:

• A petition is made to the Directorate of Naturalizations and Immigration (DIGEMIN). For this the petitioner must be resident in the Republic of Peru
  Peru
  Peru , officially the Republic of Peru , is a country in western South America. It is bordered on the north by Ecuador and Colombia, on the east by Brazil, on the southeast by Bolivia, on the south by Chile, and on the west by the Pacific Ocean....
  
  .

Foreigners can also acquire Peruvian nationality, including:

• Minor children born overseas to foreign parents who, having lived in the territory of the republic since five years of age, can elect to acquire Peruvian nationality at 18 years of age.
• Foreigners married to Peruvian spouses may acquire Peruvian nationality after two years of marriage and domicile in Peru.

Dual or Multiple Nationality

In common with many other Ibero-American countries, Peru's 1993 constitution explicitly states that nationals of Latin American countries and Spain

Spain

Spain , officially the Kingdom of Spain languages]] under the European Charter for Regional or Minority Languages. In each of these, Spain's official name is as follows:;;;;;;), is a country and member state of the European Union located in southwestern Europe on the Iberian Peninsula...

 do not lose their nationality

Nationality

Nationality is membership of a nation or sovereign state, usually determined by their citizenship, but sometimes by ethnicity or place of residence, or based on their sense of national identity....

 upon acquiring Peruvian citizenship (many Latin American countries and Spain have similar reciprocal laws). In practice, Multiple citizenship

Multiple citizenship

Multiple citizenship is a status in which a person is concurrently regarded as a citizen under the laws of more than one state. Multiple citizenships exist because different countries use different, and not necessarily mutually exclusive, citizenship requirements...

 is acknowledged and accepted by Peru and its consular and diplomatic staff.

Naturalization

A person who has 2 years of legal residency in Peru, be it by marriage or other reasons such as work, can apply for naturalization. The 2 year requirement starts from the date one acquires residency in the country, provided that residency never lapses. The years must be consecutive. If a person has a work visa that expires, and renews it later, it doesn't count as two consecutive years. The renewal must happen before the expiration of the first. For married people, simply staying in the country is sufficient.

Requirements for naturalization can be found on Peru's DIGIMEN website.

The person does not lose their previous citizenship, no letter of resignation of it is required. Unless acquiring citizenship in Peru would conflict with the former country's laws, such as for Japanese Citizens.