The Danish word opholdsbog means residence book. The plural form is opholdsbøger.
Opholdsbøger were introduced in 1875 by a law about foreigners and travelers. Immigrants, who intended to work in Denmark, had to report to the local police to obtain a residence book, which served as their work and residence permit in Denmark.1
Family tradition might tell you that you have Danish ancestors, but I have had many projects where it turned out that there were Swedish or German ancestors, too, because quite a lot of Swedes and Germans immigrated to Denmark in the 1800s.
Sources of Immigration to Denmark and Migration Within Denmark after 1874
To obtain a residence book, the immigrant had to provide id issued by a public authority.2 If the permit was granted, the police recorded information about the immigrant in a register of foreigners and travelers. Because the immigrant had to provide official id, the registers are generally a reliable source of information about an immigrant's birth year and place.
By and large, the registers are extant. They are kept by the Danish National Archives, and they are typically called one of the following names: Pasprotokol, fremmedjournal, fremmedbog, fremmedprotokol, or protokol over tilsyn med fremmede og rejsende.
When looking through the registers, you will notice that there are many listings for native Danes. The 1875 law not only required the police to keep track of foreigners, but of all travelers. If you have worked with Danish parish registers (aka church books), you might know the accession and expunction lists. The registers of foreigners and travelers replaced those lists, so they are not only useful when dealing with immigrants, but also if your ancestors moved inside Denmark.
Some registers have been imaged, but most must be viewed at the Danish National Archives. If you need assistance, feel free to contact me for an estimate of the time needed.
Above is a snippet from a register from Svaneke Town at Bornholm. The registrar noted the full name, occupation, and date and place of birth of those who moved to Svaneke. Elna Mortensen, who reported to the police on 1 May 1884, was a domestic servant born 2 September 1862 in "Store Herredstad" in Sweden. Click the image to see the full page at the website of the Danish National Archives.
When reading the foreign place names, bear in mind that the registrar had to decipher handwriting, and you know how difficult that can be, right?
- Lov om Tilsynet med Fremmede og Reisende m.m., 15 May 1875, section 3.
- Lov om Tilsynet med Fremmede og Reisende, section 1.
- The image at the top is a photograph of travelers at the Copenhagen railway station, see "Digital collections," database with images, The Danish Royal Library (https://www5.kb.dk/images/billed/2010/okt/billeder/object278717/en : accessed 18 April 2022), entry for "Rejsende på Hovedbanegården" by Holger Damgaard. The image is public domain.