The French law (Civil Code, Articles 17 and henceforth) grants French citizenship:

- To a child born to French parents; adopted by French parents; born to unknown parents (abandoned); born to stateless parents or to parents who could not grant the child their nationality.

- Every child born in France of foreign parents acquires French nationality on his coming of age where, at that time, he has his residence in France and has had his usual residence in France for a continuous or discontinuous period of at least five years, from the age of eleven.

The tribunaux d'instance, local authorities, public bodies and services and especially educational establishments are obliged to inform the public, and in particular those persons to whom paragraph 1 applies, of the provisions in force in matters of nationality. The requirements as to that information shall be prescribed by a decree in Conseil d'État.
(SOURCE: Civil Code, 21-7)

A minor child born in France of foreign parents may from the age of sixteen claim French nationality by declaration, in the way laid down in Articles 26 and following where, at the time of his declaration, he has in France his residence and has had his usual residence in France for a continuous or discontinuous period of at least five years, from the age of eleven.

Under the same terms, French nationality may be claimed, on behalf of the minor child born in France of foreign parents, from the age of thirteen and with his personal consent, in which event the requirement of usual residence in France should be fulfilled from the age of eight.
(SOURCE: ibid., 21-11)

- Marriage to a French citizen under some restrictions, see Art 21-2

- People of French cultural heritage

- French speaking alient who contributes to the society.

Source: Service-public.fr,
http://vosdroits.service-public.fr/part ... ise&l=N111