The principles about French citizenship acquisition have not changed since the middle of the xix century: a mix of "droit du sol"-"jus solis": right deriving from being born in France and "droit du sang"-"jus sanguinis": right deriving from having French ancestors. The implementations details varied though.
This is thanks to these principles that I'm French.
For more details about citizenship laws, do read "Citizenship Laws of the World" at http://opm.gov/extra/investigate/IS-01.pdf
This is very intersting, and shows how different countries have different considerations about citizenship by birth, by descent and by naturalization as well as about dual citizenship.