Hugo Theodor Horwitz lived in Berlin and Vienna and was the author of articles about the history of culture and technology. Between 1916 and 1934 he wrote regularly for the magazine Beiträge zur Geschichte der Technik und Industrie published by the Verein Deutscher Ingenieure in Berlin. In summer 1920 he married Marianne Ehrmann, born in Vienna in 1893, and their only child, Anselm Egon Horwitz, was born a year later. When the Nazis came to power in March 1938, the Horwitz family were persecuted because, despite being Catholics, they were regarded by the Nuremberg Laws as Jews. In March 1939, they had to leave their apartment at Schönburgstraße 48 in the 4th district, where they had lived since the 1920s. After changing addresses several times, Hugo Theodor and Marianne Horwitz moved in early January 1941 to Ungargasse 15 in the 3rd district. On 28 November 1941 they were deported to Minsk ghetto and murdered there, probably in July 1942. Hugo Theodor Horwitz's sister Elsa, born on 30 March 1883 in Vienna, a "patient" at the Heil- und Pflegeanstalt "Am Steinhof" in Vienna, was murdered at the Nazi "euthanasia" institute Hartheim near Linz on 6 March 1941. The only survivor of the family was Anselm Egon Horwitz, who managed to flee in April 1939 to Ireland and later emigrated to Canada. In early 1942, after Horwitz’s deportation, his library and estate was acquired by the Technisches Museum Wien. Both were returned in 2007 to his son Anselm Barnet (1921–2015). The Technisches Museum purchased the library, while the family donated the estate, with the exception of a few personal family documents, to the museum.