Many countries and national censuses currently enumerate or have previously enumerated their populations by race, ethnicity, nationality, or a combination of these characteristics. Different countries have different classifications and census options for race and ethnicity/nationality which are not comparable with data from other countries. In addition, many of the race and ethnicity concepts that appear on national censuses worldwide have their origins in Europe or in the views of Europeans, rather than in the views of the locals of these countries.

A census is the procedure of systematically acquiring, recording and calculating population information about the members of a given population. This term is used mostly in connection with national population and housing censuses; other common censuses include censuses of agriculture, traditional culture, business, supplies, and traffic censuses. The United Nations (UN) defines the essential features of population and housing censuses as "individual enumeration, universality within a defined territory, simultaneity and defined periodicity", and recommends that population censuses be taken at least every ten years. UN recommendations also cover census topics to be collected, official definitions, classifications and other useful information to co-ordinate international practices.