Population censuses provide an opportunity to count the number of inhabitants who were born outside France. Among foreign-born inhabitants, a distinction is generally made between persons born with French nationality and immigrants, who are born with a different nationality.

Inhabitants are distinguished by their nationality, i.e. French or foreign and, among French citizens, those who were born French and those who have been naturalized. The census provides information on current nationality and nationality at birth.

Foreigners and immigrants form two different categories. Immigrants "born abroad as a foreign national" may still be foreigners at the time of the census or may have become French. Foreigners, for their part, may have been born abroad (in which case they are immigrants) or in France (in which case they are not immigrants).