Jascha Horenstein (May 6 [O.S. April 24] 1898 in Kiev - April 2, 1973 in London) was a conductor.

Horenstein was born in Kiev; his mother was Austrian. His family moved to Vienna in 1911 and he studied there with Joseph Marx (music theory) and Franz Schreker (composition) before moving to Berlin and working as an assistant to Wilhelm Furtwängler. During the 1920s he conducted the Vienna Symphony Orchestra and the Berlin Philharmonic Orchestra. Forced as a Jew to flee the Nazis, he moved to the United States of America in 1940 (he eventually became an American citizen). He died in London.

Horenstein is particularly remembered for championing modern music (in 1929 he conducted the premiere of the arrangement for strings of three movements of Alban Berg's Lyric Suite), and for his advocacy of the works of Anton Bruckner and Gustav Mahler at a time when both composers were very unfashionable; his 1951 Vox recording of Mahler's Ninth Symphony was the first commercial record of that now oft-recorded work. He gave the first (concert) performance of Berg's Wozzeck in 1950. He recorded Mahler's Das Lied von der Erde in 1972 and all of Mahler's symphonies apart from the 2nd and 5th, and Robert Simpson's 3rd Symphony during 1969 to 1971.