Paul Tietjens (22 May 1877 – 25 November 1943) was an American composer of both popular and serious music in the first half of the twentieth century. His greatest success came when he composed music for the 1902 stage adaptation of L. Frank Baum's The Wizard of Oz.

Tietjens was born in St. Louis (as was, coincidentally, Baum's other main composer, Louis F. Gottschalk). He followed a course of study in classical music, and debuted as a piano soloist with the St. Louis Symphony at the age of fourteen. He later studied in Europe with several teachers.

At the start of his career Tietjens deliberately set out to establish himself as a composer of comic operas and operettas. He approached Baum in March 1901, not long after the initial success of The Wonderful Wizard of Oz. By one report, the two men were introduced by Chicago newspaper artist Ike Morgan, who worked on Baum's American Fairy Tales. By another account, Tietjens simply rang Baum's doorbell one evening. Baum also was eager for stage success, and the two men began working on potential projects.

Oddly enough, their first efforts did not involve Oz. They wrote a show called The Octopus or Have a Little Trust, which was rejected by producers in Chicago and New York. Their next endeavor, King Midas, was never completed. It was Oz illustrator W. W. Denslow who suggested an Oz adaptation. The three men collaborated on the show, with Denslow designing the sets and costumes (his full one-third share of the royalties became a source of conflict among the three). Tietjens economically recycled two songs from The Octopus, "Love is Love" and "The Traveler and the Pie," into the Oz show.

Upon its debut in 1902, the show was a tremendous hit; it played until 1907 and then toured widely, making Tietjens financially independent at a young age. In addition to Tietjen's music, the show incorporated music from other songwriters, as was typical practice at the time. A. Baldwin Sloane and Nathaniel D. Mann were among a score of songwriters whose work eventually was used in the play.

Though he tried, Tietjens was never able to reproduce the same kind of popular success later in his career. He spent much of his later life in Europe, but returned to St. Louis to die in 1943.

Baum borrowed Tietjens's name for his comical composer Tietjamus Toips in John Dough and the Cherub.

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