A birth outside marriage usually does not end a line; it moves the proof from a marriage certificate to an acknowledgement of paternity, and in two countries it needs a declaration or a registration to be repaired. An adoption is the opposite case: it can start a line into the adoptive parents’ citizenship and end the one from the birth parents, on the same day.
Both are more often fixable than readers fear, and both turn on a document rather than on a family story. Here is which document, for which country, and the two places this genuinely becomes a matter for a lawyer.
Two facts with opposite effects
Keep them apart, because they are usually discussed together and they behave differently.
Born outside marriage. The biological link is there and the legal link has to be shown. Historically several of these countries passed citizenship from an unmarried mother but not from an unmarried father, so the break is almost always on the father’s side and almost always repairable today.
Adopted. The legal link is created and another is severed. Which citizenship follows depends on the country of the adoption order, the law in force on its date, and the age of the child, and the answer can be that one line opens while another closes.
Born outside marriage: Britain, before 1 July 2006
Britain is the clearest case, and it has a statutory route.
A child born before 1 July 2006 to a British father who was not married to the mother did not acquire British citizenship from him. The Immigration Act 2014 created a registration route for exactly those people, inserting sections 4F to 4I into the British Nationality Act 1981, in force from 6 April 2015.
Section 4G states the test plainly: it applies to a person who “would have automatically become a British citizen at birth by the operation of any provision of this Act or the British Nationality (Falkland Islands) Act 1983, had P’s mother been married to P’s natural father at the time of P’s birth.” Checked against legislation.gov.uk on 15 September 2026.
The section also carries a consent requirement where the applicant is under 18: consent from both natural parents “in the prescribed manner”, or from the survivor where one “died on or before the date of the application.”
One caution, and it is the same one that limits every British repair: citizenship acquired this way is generally British by descent, and a British citizen by descent cannot ordinarily pass citizenship to a child also born outside the UK. The route reaches the person registering. The British line sets out why, and double descent is the narrow gap where a grandparent’s line still passes.
Born outside marriage: Germany, and the acknowledgement that must exist
Germany passes citizenship from an unmarried father, and it is strict about the paperwork and about the clock.
From 1 July 1993, a child born outside marriage to a German father acquires German citizenship at birth where paternity is legally established. Section 4(1) of the Staatsangehörigkeitsgesetz requires the acknowledgement or judicial establishment of paternity to be effective under German law, and to have been made or at least initiated before the child turned 23. That deadline is the part that catches people: an acknowledgement obtained at 30, for a link everybody in the family always knew about, is too late for this route.
For births before that date, and for lines broken by the old legitimation rules, the route is the declaration under section 5 of the Staatsangehörigkeitsgesetz. Its wording covers “Kinder eines deutschen Elternteils, die durch Geburt nicht die deutsche Staatsangehörigkeit erworben haben” — children of a German parent who did not acquire German citizenship at birth — and separately “Kinder, die ihre durch Geburt erworbene deutsche Staatsangehörigkeit durch eine von einem Ausländer bewirkte und nach den deutschen Gesetzen wirksame Legitimation verloren haben”: children who lost German citizenship, acquired at birth, through a legitimation effected by a foreigner. And it reaches “Abkömmlinge” — descendants — of those children. Checked against the Staatsangehörigkeitsgesetz on 15 September 2026.
That second category is a genuinely strange break worth naming: a child who was German at birth could lose it because a foreign man legitimated them. Section 5 is the repair, it reaches the descendants, and it has a deadline of ten years from the amending Act’s entry into force in August 2021. The declaration route.
Born outside marriage: Italy, Ireland, Poland and Canada
Shorter, because in these four the question is usually evidential rather than substantive.
Italy. The link is made by the Italian parent’s recognition of the child, and the consulate or the comune reads the recognition document and its date. Where the Italian ancestor is the mother, the maternal cut-off of 1 January 1948 may apply instead and that is a different problem — the grandmother's line.
Ireland. Entitlement through a grandparent turns on that grandparent’s birth on the island of Ireland, so the substantive rule is untouched. What changes is the chain of certificates: the Department of Foreign Affairs has to be satisfied of each parental link, and where a birth certificate names no father, that link is proved some other way. The Status of Children Act 1987 removed the distinction between children born inside and outside marriage in Irish law; for a birth before it, ask the Department what it will accept rather than guessing. The current procedure is on its Foreign Births Register pages, and the chain of certificates is the order to get them in.
Poland. A child of an unmarried Polish mother generally took her citizenship under the Act of 20 January 1920, so the maternal line is the usual route. The Polish difficulties lie elsewhere — whether the ancestor was ever a Polish citizen, and the loss rules. The Polish line.
Canada. Children born abroad outside marriage under the older Acts are one of the groups the 2009 and 2015 amendments were written to reach, and some were restored by them. The Canadian line is the verdict, including where the generation limit stops a line the amendments would otherwise have carried.
Adoption can open one line and close another
An adoption order does two things at once, and a reader who has one in the chain has to ask about both.
It can create a line. Germany gives German citizenship to a child adopted by a German under section 6 of the Staatsangehörigkeitsgesetz, where the child is a minor at the time the adoption is applied for. Ireland treats the adopted child of an Irish citizen as an Irish citizen. Most of these countries have an equivalent, and in each the age of the child and the date of the order are the conditions.
It can end one. Section 27 of the Staatsangehörigkeitsgesetz provides for loss of German citizenship by adoption by a foreigner, and the German missions list adoption among the ways German citizenship is lost — one of four headings on their own page on the subject, beside voluntary acquisition of another citizenship, voluntary service in a foreign army and renunciation. Checked on 15 September 2026.
So a German child adopted by an American couple in 1960 may have ceased to be German that year, and the line to everyone below them ended there rather than at any naturalisation. Nothing in the family papers will look like a citizenship document; it will look like an adoption file.
The documents that answer it
Three, and in this order:
- The full birth certificate of the link in question — the long form, which shows what the register actually recorded about both parents, rather than the short form, which often shows neither. The chain of certificates is the order to request them in.
- The acknowledgement of paternity, or the court order establishing it, with its date. For Germany this is the document the 23-year rule is measured against.
- The adoption order, with the country and the date, where there is one.
With those three, most of the cases on this page answer themselves against the rules above.
Where this becomes a matter for a lawyer
Twice, and they are worth paying for.
An adoption anywhere in the chain. Two legal systems interact — the adoption’s and the citizenship’s — and the outcome turns on how the adopting country’s order is characterised under the other country’s law on its date. That is not a form; it is an opinion.
A paternity link that was never legally established and now cannot be. Where the acknowledgement was never made, the father has died, and a country’s own deadline has passed, whether anything remains is a question for somebody who practises in that jurisdiction.
For everything else here, a register takes a form and you do not need anybody. Which claims need a lawyer draws the line, and the seven breaks puts this one beside the six others so you can check that nothing earlier in the chain ended the line before this ever came up.