Most citizenship-by-descent rules were written for one kind of family: married parents and a biological child. If you, a parent or an ancestor was born to unmarried parents, or was adopted, the usual rules can work differently. Where our guides cover it, children of unmarried parents are now treated the same once paternity is established, and several countries make adopted minors citizens. The trouble is older births, where the rules of the time still decide.
This page gathers what our country guides and the official sources we read say. It is deliberately limited to that. Where a guide says nothing about adoption or birth outside marriage, we say so: that doesn’t mean there is no rule, only that you need to ask the authority directly.
The short answer
- Born to an unmarried mother who was a citizen: the guides we have don’t describe a problem here, and in Poland and pre-1984 Greece this was actually the case in which a mother could pass on citizenship.
- Born to an unmarried father who was a citizen: this is the common gap. The UK, Germany, Sweden, Denmark, Switzerland and Liechtenstein all had one, and most now have a fix. You will almost always need proof of paternity.
- Adopted as a child by a citizen: the Netherlands, Germany, Italy and Sweden make adopted minors citizens, with conditions. Germany’s law says citizenship acquired by adoption extends to the adoptee’s descendants; for other countries, ask.
- Adopted away from a citizen birth parent: none of our guides addresses whether this ends the citizenship that came through the birth parent. Ask the authority.
If a child was born to an unmarried father
Older laws often gave the child of unmarried parents only the mother’s citizenship. If the father was the citizen, the line could stop. Here is what each guide says.
- United Kingdom
Before 1 July 2006 a British father who wasn’t married to the mother generally couldn’t pass on citizenship. Sections 4F to 4I let those children register on Form UKF if they would have been British had the parents been married. You need proof of paternity; the Home Office says DNA must not be demanded.
Form UKF and Form UKM explained → - Germany
Children born outside marriage after 23 May 1949 and before 1 July 1993 to a German father and a non-German mother can declare under § 5 StAG by 19 August 2031, if the parents weren’t married to each other before 1 July 1998 and paternity was recognised, or proceedings began, before the child turned 23. Descendants can declare too.
§ 5 StAG declaration → - Sweden
For births from 1 April 2015, marriage makes no difference. Before then, a child born abroad to a Swedish father not married to the mother wasn’t automatically Swedish; Migrationsverket says the father needs to file a notification. If the parents later married while the child was under 18 and unmarried, the child became Swedish on the wedding date.
- Denmark
For births from 1 July 2014, marriage makes no difference. A child born abroad before then to an unmarried Danish father didn’t automatically become Danish. Our guide doesn’t set out the remedy; ask the Danish authorities.
- Finland
A child of a Finnish father married to the mother is Finnish; otherwise once paternity is legally established. A child born abroad to an unmarried Finnish father may need a declaration.
- Iceland
A child of an Icelandic father is Icelandic if the parents were married, or once paternity is established under the rules in force at the birth. Older cases may not have acquired it; ask the Directorate of Immigration about notification.
- Switzerland
Children of unmarried Swiss fathers born before 2006 didn’t automatically become Swiss, but can apply for facilitated naturalisation (Article 51).
- Liechtenstein
Children of unmarried Liechtenstein fathers acquire citizenship through a facilitated procedure once paternity is established.
- Austria
A child is Austrian at birth through an Austrian mother, or an Austrian father married to the mother. For an unmarried Austrian father, paternity must be established in time.
- Netherlands
The IND says a child acknowledged by a Dutch citizen after 1 March 2009 becomes Dutch if acknowledged before age 7. From 7 to 18, a DNA test from an accredited laboratory within a year and three years’ care are also needed. Acknowledgments from 1 April 2003 to 1 March 2009 follow a separate scheme; ask the municipality or embassy.
- Italy
Under Article 2 of Law 91/1992, recognition or a court declaration of parentage while the child is a minor decides citizenship under the law. An adult recognised later keeps their status but can elect the citizenship that follows within one year.
- Greece
Before 8 May 1984 a Greek mother could pass citizenship to a child born outside marriage, even though she generally couldn’t to a child born in marriage to a foreign father. Some older cases need a declaratory decision under Article 26, for example a child born before 18 July 1982 to a Greek father and a foreign mother.
Greek citizenship through grandparents → - Poland
Under the 1920 Act, a child born in marriage took the father’s citizenship, and a child born outside marriage took the mother’s. That cuts both ways in an old line: it can carry a Polish mother’s citizenship, or fail to carry a Polish father’s.
Polish citizenship confirmation →
Legitimation could also take citizenship away. In Germany, a child born to a German mother after 23 May 1949 and before 1 April 1953 could lose German citizenship if the foreign father later married the mother; § 5 StAG covers those children too. Hungary’s 1879 Act listed legitimation among the ways citizenship ended. If an ancestor’s parents married after the birth, check the rule of that time.
If you or an ancestor was adopted
Adoption usually works as a separate way of acquiring citizenship, not as descent, so its rules have their own conditions on age and on what kind of adoption counts.
- Netherlands
The IND says a child becomes Dutch automatically by adoption if under 18, one adoptive parent is Dutch, the adoption follows the Hague Adoption Convention or Book 10 of the Dutch Civil Code, and legal ties with the original parents are completely broken.
- Germany
§ 6 StAG: a child under 18 when the adoption application is made, adopted by a German in a way valid under German law, becomes German, and so do the child’s descendants. A foreign adoption counts only if it ended the legal tie to the birth parents and equals a German adoption (or is converted under the Adoption Effects Act).
- Italy
Article 3 of Law 91/1992: a foreign minor adopted by an Italian citizen acquires citizenship, including people adopted before the law took effect in 1992. Since Law 74/2025, one of the new conditions refers to a parent or adoptive parent who lived in Italy for two years before the child’s birth or adoption.
Italy’s 2025 conditions → - Sweden
Migrationsverket: a child under 12 adopted by a Swedish citizen becomes Swedish automatically if the adoption was decided in a Nordic country, or a foreign decision was approved in Sweden by MFoF, after 30 June 1992. A child adopted at 12 or older can apply.
- United Kingdom
A parent adopted in the UK counts like one born there when passing on citizenship to a child born abroad. GOV.UK lists being adopted outside the UK as a case where you may be able to apply. For section 4C, a mother who was a citizen by adoption in the UK counts.
- Ireland
If a parent or grandparent was adopted, extra documents apply, and the Department of Foreign Affairs asks people claiming through an adoptive rather than a biological link to contact it before applying to the Foreign Births Register.
Irish passport through grandparents → - Austria
Under § 58c (descendants of people persecuted by the Nazi regime), children adopted while they were minors count as descendants. Our guide doesn’t cover adoption for ordinary descent.
Austria § 58c → - Luxembourg
The Article 23 option is open to an adult whose parent or adoptive parent holds or ever held Luxembourg nationality and didn’t pass it on.
Luxembourg Article 23 →
Adoption also comes up in dual citizenship rules. Our guides record that Slovakia doesn’t take away citizenship from someone who acquires another nationality by adoption, that Latvia lets citizens keep a nationality acquired automatically through adoption, and that Lithuania lists children adopted by Lithuanian citizens, and Lithuanian children adopted abroad, among its dual citizenship cases.
Where our guides are silent
We won’t fill gaps with guesses. Our guides don’t state adoption or legitimacy rules for Spain, Portugal, Hungary (beyond the 1879 legitimation rule), the Czech Republic, Croatia, Romania, Lithuania and Latvia (beyond dual citizenship), Norway, France (where our checker only notes that pre-1973 legitimacy rules need case-by-case analysis) or most other countries. Adoption isn’t covered for Denmark, Finland, Switzerland, Greece or Poland either. In those cases, write to the citizenship authority or the consulate before you pay for records, and describe the adoption or the birth outside marriage up front. The Greek guide gives the same advice: if anything in your family looks irregular, tell the consulate in full at the start.
The documents these cases need
Beyond the usual birth and marriage records for every generation, expect to be asked for:
- Proof of paternity for an unmarried father: an acknowledgment, a court decision, or a birth certificate naming him. For Form UKF, the Home Office accepts a birth certificate naming him issued within 12 months of the birth before 10 September 2015, or other evidence such as DNA reports or court orders.
- The adoption order, and for a foreign adoption, proof it is recognised in the country you are claiming: the IND, Migrationsverket and § 6 StAG all set conditions on foreign adoptions.
- The parents’ later marriage certificate if legitimation is part of the story (Sweden, Germany).
- Name-change records, since adoption and legitimation often change a surname. Germany’s BVA and Austria’s § 58c lists both ask for adoption papers and paternity documents where they apply.
Our guide to building a document chain, documents checklist and apostille guide cover the rest. For lines that run through a woman, see citizenship by descent through your mother, and to test your line against each country’s rules, try the free eligibility checker.
Frequently asked questions
Can you get citizenship by descent if your parents weren’t married?
Usually yes today, but older births may need a step. Several countries once stopped unmarried fathers passing on citizenship: the UK before July 2006, Germany before July 1993, Denmark before July 2014, Sweden before April 2015, and Switzerland before 2006. Most of these now offer registration, a declaration, a notification or facilitated naturalisation, and you will need proof of paternity.
Can an adopted child get citizenship by descent?
Often, but through the adoption rather than descent. The Netherlands, Germany, Italy and Sweden grant citizenship to children adopted by their citizens, with conditions on age and the kind of adoption: under 18 for the Netherlands and Germany, a minor for Italy, under 12 for automatic Swedish citizenship. The Dutch, German and Swedish rules set conditions on foreign adoptions. For other countries, ask the authority.
Can I claim citizenship through my adopted grandparent?
Only if that grandparent actually became a citizen through the adoption, or was one already, and passed it on. Germany’s § 6 StAG says citizenship acquired by adoption extends to the adoptee’s descendants. Ireland’s Department of Foreign Affairs asks people claiming through an adoptive link to contact it first. Our other guides don’t address adopted ancestors, so ask the authority before you order documents.
Can I get British citizenship if my British father wasn’t married to my mother?
Yes, if you were born before 1 July 2006 and would have been British had your parents been married. You register under sections 4F to 4I on Form UKF. Sections 4G to 4I charge only the ceremony fee; 4F carries a full fee and a good character test from age 10. You need proof of paternity, but the Home Office says DNA must not be demanded.
Can I get German citizenship through my unmarried German father?
Yes, by declaration, if you were born after 23 May 1949 and before 1 July 1993 to a German father and a non-German mother who weren’t married to each other before 1 July 1998, and paternity was recognised or proceedings began before you turned 23. The § 5 StAG declaration is free and must reach the BVA by 19 August 2031. Children born from July 1993 were generally German at birth.
Does DNA testing prove descent for citizenship?
Sometimes it’s required, sometimes it must not be. The Netherlands requires a DNA test from an accredited laboratory when a Dutch citizen acknowledges a child aged 7 to 18. The UK accepts DNA reports as one kind of proof of paternity for Form UKF but says DNA must not be demanded. Other guides don’t say, so ask the authority what evidence it accepts.
Official sources
- IND (Netherlands): Dutch citizen by birth, acknowledgment or adoption (adoption conditions, acknowledgment after 1 March 2009, DNA test)
- § 6 Staatsangehörigkeitsgesetz (StAG): acquisition by adoption
- Bundesverwaltungsamt: Erklärungserwerb (§ 5 StAG) (unmarried German fathers, legitimation)
- Law 91/1992 (Normattiva) (Article 2, recognition of parentage; Article 3, adoption of minors)
- Migrationsverket (Sweden): automatic citizenship for children (adoption, unmarried fathers before 1 April 2015, legitimation)
- GOV.UK: apply for citizenship if you have a British parent (adoption, unmarried parents, by birth period)
- GOV.UK: Form UKF
Checked against these sources on 29 October 2026. The IND, GOV.UK, Migrationsverket, § 6 StAG and Law 91/1992 texts were read directly on that date. The Irish Department of Foreign Affairs and Irish statute pages could not be opened, so the Irish line is as our Irish guide states it. Other lines restate our country guides and their sources. This is general information, not legal advice; adoption and paternity cases turn on their facts, so confirm with the relevant authority before you apply.