[Xixi]

A little technicality: persons born in France are automatically granted French citizenship at 18, providing that they are living in France at 18, and have lived in France for at least 5 years previously. These criteria tend to change a lot as this is a rather sensitive topic in France. Also sometimes an application is necessary, sometimes not.

An odd case: if both parents are foreigners, but one of them is born in France, then their children will automatically become French at birth (if born in France).

Then there are special rules for Algeria, as it was a part of France until 1962...