For digital societies to function, personal identifiers are useful, if not unavoidable. Quite an array of public services rests on the premise of identitfication and authentication of the citizens – the quality of that process determines the quality of the services, in many cases. According to the World Atlas, there are currently 195 countries in the World. According to the data we have collected from the official sources and related Wikipedia articles, half of the countries have already implemented a kind of unique identifier for their citizens, residents, visitors or (why not the) e-residents. The names for the identifiers vary – depending on the country this attribute can be called Personal Identification Number or Citizen Number or Resident Registration Number or just Taxation ID. What will follow, is a short overview of the essence of personal identifiers and also the history of introducing these.