Carl Robert Osten-Sacken or Carl-Robert Romanovich, Baron von der Osten-Sacken, Baron Osten Sacken (21 August 1828, – 20 May 1906) was a German-Russian diplomat and entomologist. He served as the Russian consul general in New York City during the American Civil War, living in the United States from 1856 to 1877. He worked on the taxonomy of flies in general and particularly of the family Tipulidae (crane flies).