Leo Flieg (5 November 1893 – 15 March 1939) was a German politician, and a founder member of the Communist Party of Germany, regarded by some as an "Éminence grise" to the national leadership.
He served as a member of the Prussian regional parliament ("Provinziallandtag") between 1924 and 1933.
In 1938 he was arrested in Moscow where he had lived for some years.