Tadeusz Zygfryd Kassern (Lemberg, Austro-Hungarian Empire, 19 March 1904 – New York City (United States), 2 May 1957) was a Polish composer of Jewish origin.
In the Nazi occupied parts of Poland Kassern was using false identity papers to protect himself from the Gestapo.
In the post-war years, he served as a cultural attaché in New York to the new Polish government.
In 1948 Kassern, after a brief visit to the communist-ruled Poland, suddenly resigned his position, renounced his Polish citizenship and applied for US asylum.
Among Kassern's well known students was the Italian-born American composer Dalmazio Santini (1923-2001).