Finland - Passport & Nationality - Finnish Citizenship by Descent

A child acquires Finnish citizenship at birth if:

The child's mother is a Finnish citizen;
The child's father is a Finnish citizen and the parents are married;
The child's father is a Finnish citizen, the child is born out of wedlock, and paternity has been established;
The child's father who died before the child was born was a Finnish citizen and who was married to the child's mother at the time of his death; or
The child's father, who died before the birth of the child, was a Finnish citizen and the child was born in Finland out of wedlock and the father's paternity was established.

A child who is born abroad and whose father is a Finnish citizen will acquire Finnish citizenship when the parents get married. If paternity has been established, the child will acquire Finnish citizenship as of the date of the marriage contract. If paternity is established after this point, the child will acquire Finnish citizenship as of the date on which paternity is established.