Sweden - Passport & Nationality - Swedish Citizenship by Descent
The child's mother is a Swedish citizen (Swedish mothers have only been able to pass on their citizenship since 1 July 1979);
the child's father is a Swedish citizen and is married to the child's mother;
the child's father is a Swedish citizen, the child is born out of, and the child is born in Sweden.
A child who is born abroad and whose father is a Swedish citizen (not married to the child's mother, and the mother is not Swedish) will acquire Swedish citizenship when the parents get married, provided the child is aged under 18.