Christian Friedrich Georg Wilhelm Oncken (19 December 1838 – 11 August 1905) was a German historian.

After his early education, Oncken studied classical philology, history and philosophy in Heidelberg, Göttingen and Berlin.

He remained at Gießen for his entire career, declining an appointment to the University of Königsberg in 1873, and served as its chancellor in 1877-78.

Oncken published his most famous work, Allgemeine Geschichte in Einzeldarstellungen [de] (Common History in Monographs) in 44 volumes, issued from 1876 to 1891.

He delivered countless public lectures on the history of Germany, held throughout the country.