Germany has begun its first census since reunification, in line with European Union wishes that all member states carry out a population count this year.
The last census in West Germany was conducted in 1987; the last one in East Germany in 1981.
The EU wants all 27 member states to carry out population counts every ten years to ensure it has proper statistics.
Germany's census will be carried out both by direct polling of some 10% of the population by some 80,000 enumerators, and by the collating of data already held by authorities, including home registrations.
At the time of the last census in West Germany, officials had attempted to directly survey every resident in the country.
Questions asked range from age to sex, education to home ownership, but also focus on issues such as religion and ethnic origin.
As in previous censuses, questions have been raised about data privacy.
Authorities require that most of their questions be answered, but have promised to strictly protect anonymity.
Germany's population has been ageing and decreasing since 2003, and official figures issued early this year put its number at 81.7m.
But officials believe this might be over-estimated, by perhaps as much as 1m, especially in eastern Germany, as many people have moved west since reunification of the country in 1990.
The first census was carried out in what was then the German Empire in 1871.
