Luxembourg nationality law is ruled by the Constitution of Luxembourg. The Grand Duchy of Luxembourg is a member state of the European Union and, therefore, its citizens are also EU citizens.
Nationality by birth
Luxembourg law generally follows jus sanguinis with limited jus soli provisions. Citizenship is automatically given to: a child of a Luxembourg citizen parent, regardless of the place of birth; a child born in Luxembourg to a parent born in Luxembourg (even if the parent is not a Luxembourg citizen); or a child born in Luxembourg to parents who are stateless or unable to pass their nationality onto their child; or a child born in Luxembourg to unknown parents. Furthermore, a child born in Luxembourg to foreign parents, neither of whom were born in Luxembourg, gains Luxembourg citizenship automatically upon turning 18 years old if: at least one of their parents lived continuously in Luxembourg in the 12 months preceding their birth; and they have lived continuously in Luxembourg in the 5 years immediately preceding their 18th birthday.
Naturalization
Naturalization is permitted, subject to the following conditions: being at least eighteen years old; five years of legal residence in the Grand Duchy, including an uninterrupted period of one year immediately before applying for citizenship; passing a Luxembourgish language exam; taking a course on "living together in the Grand Duchy" or passing the associated examination; and never having been given a custodial sentence of 12 months or more or a suspended custodial sentence of 24 months or more, in Luxembourg or any other country, for an action that would constitute a crime under Luxembourgish law, provided that the sentence was not fully served within the fifteen years before the application for naturalization
Acquisition of nationality by option
Luxembourg law also provides for the possibility to acquire nationality by option, which is a separate legal concept from naturalization.
Obtaining nationality by option is permitted in the following ten cases: Adults with a parent (biological or adopted) or grandparent who is/was a Luxembourger and was unable to pass Luxembourg nationality to the person at birth (e.g. due to the nationality laws of another country forbidding it); Parents of Luxembourg minors (requires 5 years' residency and passing the Luxembourgish language and integration exams); Persons who are married to a Luxembourg citizen (requires passing the Luxembourgish language and integration exams; no minimum residency or marriage length requirement for spouses living in Luxembourg; 3 years' marriage required for spouses living outside Luxembourg); Persons aged 12 or above who were born in Luxembourg and did not automatically become a citizen at birth due to neither of their parents being Luxembourg citizens or born in Luxembourg (requires 5 years' residency and for at least one parent to have lived continuously in Luxembourg for at least 12 months immediately prior to the person's birth); Adults who have completed at least 7 years' schooling in Luxembourg (requires 12 months' residency immediately prior to the citizenship application); Adults who have legally resided in Luxembourg for at least 20 years (requires 12 months' residency immediately prior to the citizenship application and a total of 24 hours' attendance at a Luxembourgish language course, but no requirement to pass the language exam); Adults who have fulfilled the obligations of the Welcome and Integration Contract (Contrat d'accueil et d'intégration), a free, optional course available to any foreigner living in Luxembourg (also requires 5 years' residency and passing the Luxembourgish language and integration exams); Adults who settled in Luxembourg before turning 18 (requires 5 years' residency and passing the Luxembourgish language and integration exams); Adults who are stateless, refugees or have subsidiary protection status (requires 5 years' residency and passing the Luxembourgish language and integration exams); or Volunteer soldiers who have completed one year of good and loyal service, as certified by the Luxembourg Army's Chief of Staff.
All of the options also have the same "good repute" requirements as for naturalisation, i.e. the applicant must never have been handed an immediate custodial sentence of 12 months or more or a suspended custodial sentence of 24 months or more, in any country.