EXPAT FAQ
https://www.easyexpat.com/en/faq.htm
How to get the French nationality?
You can get French citizenship by 2 ways:
A/ Awarding:- filiation (to be a direct descendant of somebody) called also droit du sang: Is French a child from one French parent at least.
- being born on the French territory called also droit du sol: Is French a child born in France AND from a parent born in France.
B/ Naturalization:
- Is French a child born in France and living in France for a certain period.
- Is French a person marrying a French one.
- Is French a child adopted by at least one French parent.
- Is French a person having lived in France for 5 years and with decision of the administration.
- Is French a child (less than 18 years old) when one of his/her parent gets the French citizenship.
[source : http://www.diplomatie.gouv.fr]