The German National Library has published German phone directories from 1915 to 1981 online, aid those who are tracing their ancestors.
The directories will be of global interest because millions fled Germany after the Nazis’ rise to power.
Many also left after the First World War, during the Great Depression and after the Second World War.
Nearly three million Britons claim German heritage.
Physicist Einstein is listed in the 1930 Berlin directory. Hitler’s mistress Eva Braun is listed in the 1937 Munich directory.