Hans-Werner Janssen (1 June 1899 – 19 September 1990) was an American conductor of classical music, and composer of classical music and film scores.
Janssen was born in New York City on 1 June 1899. His father was the famous New York restaurateur of the Hof Brau Haus and encouraged Werner to enter the family business, opposing the son's desire for a musical career. Therefore, after Werner completed secondary school (graduating from Phillips Exeter Academy) he had to support his own musical education at Dartmouth College. He did this by being a waiter, performing in cabarets and theaters, and selling his own popular compositions. At the New England Conservatory of Music he studied with the composers George Chadwick and Frederick Converse. He also studied piano with Arthur Friedheim, a pupil of Franz Liszt.
Janssen entered the US military (infantry) in World War I. After the war he returned to his studies and earned a bachelor's degree in music at Dartmouth College in 1921. He began to compose jazz songs for Tin Pan Alley. He made recordings as a pianist of two of his popular songs in 1920. He composed for the Ziegfeld Follies of 1925 and 1926 and wrote several songs which became national hits. This helped finance his conducting studies with Felix Weingartner in Basel, Switzerland (1920–21) and with Hermann Scherchen in Strasbourg, France (1921–25). He also received a Juilliard Fellowship and the Rome Prize from the American Academy in Rome for his tone poem for large orchestra in a jazz idiom New Year's Eve in New York. That composition received its premiere from the Rochester Philharmonic Orchestra conducted by Howard Hanson on May 8, 1929. In 1930, it was performed by the Cleveland Orchestra conducted by Nikolai Sokoloff, and was recorded in 1929 by The Victor Symphony Orchestra conducted by Nathaniel Shilkret. Shilkret and Janssen were later (1945) to exchange roles, with Janssen and his Symphony Orchestra of Los Angeles conducting the Genesis Suite which was conceived of and coauthored by Shilkret.