In connection with professional texts, statistics, encyclopedic entries or other information about ethnic communities, data on their abundance are also commonly mentioned. However, an apparently straightforward fact as ethnicity/ethnic identity, seemingly easy to measure exactly, is highly debatable, as it hides a number of pitfalls and difficult-to-answer questions. The same applies to the no less vague and difficult-to-measure phenomena of knowledge/use of language or mother tongue and their registratio.
The tradition of ethnic/linguistic censuses is strong especially in Central and Eastern Europe. The author documents this fact on the Czech example, which is still based on the Austro-Hungarian model. The main emphasis of the text is on the current specific problems of ethnic and linguistic records, which are documented and analyzed: 1/ at a general level; 2/ on several current examples of European minority ethnic groups (Welsh, Sámi, Sorbs, Kalmyks, Ruthenians).
It follows from the above that the standard publication of results of ethnic and linguistic censuses - despite their widespread and apparent exactness - must be received with considerable caution.