David Jacob Simonsen (Hebrew: דוד יעקב סימונסן; 17 March 1853 – 15 June 1932) was born in Copenhagen, Denmark.

He studied Oriental languages at the University of Copenhagen, and received his rabbinical training at the Jewish Theological Seminary in Breslau, one of the centres for "Wissenschaft des Judentums", a movement advocating the scientific study of Jewish history, literature, and culture in addition to the classical sources of Judaism.

The list of correspondents contains the names of leading scientists within Oriental and Jewish Studies but also from other areas, such as the classicist Ada Adler.

[1][2] During World War I, Simonsen acted as "communication central", maintaining all the important contacts in Denmark and abroad, between organisations and individuals.

He was also able to relay messages between relatives on different sides of the front, and after the war, he continued to be active in different relief organisations, both in Denmark and abroad.