Józef Unszlicht or Iosif Unshlikht (Russian: Ио́сиф Станисла́вович У́ншлихт; nicknames "Jurowski", "Leon") (December 31 [O.S. 19 December] 1879 in Mława, Płock Governorate - July 28, 1938 on a shooting range in Moscow Oblast), a Bolshevik revolutionary activist, one of the founders of the Cheka, and Soviet government official of Polish-Jewish extraction from the Masovian region. Unschlicht participated to and in fact initiated some of the worst excesses of the Bolshevik revolution including mass murders of political opponents. In 1924, he was replaced by Genrikh Yagoda who continued and amplified Unschlicht's previous policies.

A member of Social Democracy of the Kingdom of Poland and Lithuania from 1900 and the Russian Social Democratic Labour Party from 1906 (following their merger), Unszlicht took part in Vladimir Lenin's October Revolution and in 1918 joined the Red Army.

In 1919 Unszlicht served briefly as an authority in Lithuania and Belarus, and in 1920 joined the Politburo of the Communist Party. During the Polish-Soviet War in August 1920 he became a member of Provisional Polish Revolutionary Committee, the Bolshevist puppet government of Poland in Białystok.

His brother, Julian, was a journalist who "fought against the socialist movement in general and especially against Jewish involvement in it." In later years, Julian converted to Catholicism and joined the priesthood.

Józef Unszlicht was arrested in 1937, during the Great Purge, and executed in 1938.