In 1920, Oscar Hammerstein II—fresh from the modest success of his debut musical Always You—was eager to write the show for Frank Tinney that his uncle Arthur was to produce. As Hugh Fordin wrote, “Arthur, confident of his nephew's ability but aware that he needed to learn more about his craft, brought in Otto Harbach to collaborate on the book and lyrics.” The two men joined forces on that show—Tickle Me—and went on to write such classics as Rose-Marie (1924, Rudolf Friml & Herbert Stothart), Sunny (1925, Jerome Kern), and The Desert Song (1926, Sigmund Romberg). After working with Harbach (Fig. 1), Hammerstein would venture on his own and write Show Boat, Oklahoma!, and be credited as having ushered in a new era of musical theatre, chiefly defined by his success at “integration.” As literary scholar Scott McMillin writes, the conventional idea of integration is that “all elements of a show—plot, character, song, dance, orchestration, and setting—should blend together into a unity, a seamless whole.” In popular commentary, this development is often attributed to Rodgers & Hammerstein's 1943 musical Oklahoma!, as seen in John Kenrick's claim that “[t]hroughout the show, every word, number, and dance step was an organic part of the storytelling process. Instead of interrupting the dialogue, each song and dance continued it. For the first time, everything flowed in an unbroken narrative line from overture to curtain call.” Other historians and critics are more tempered, touting the success of Oklahoma! while insisting that its integration must be seen as part of a broader historical arc. Andrew Lamb, for example, celebrates Oklahoma! by noting that it was the realization of “[w]hat Kern and Gershwin had experimented with as far back as the 1920s—a piece that was not just a collection of catchy numbers, but a fusion of drama, song, and dance.” In a 1962 article, Stanley Green notes that the creators of Oklahoma! “blended all the theatrical arts with such skill tha[t] many accepted it as a revolution in the theatre,” but he argues that their accomplishment was actually “more evolutionary than revolutionary. Rather than inaugurating any trend toward the well-integrated show, what it did achieve was a perfection in technique of a development that had been going on ever since the second decade of the century.” While Green cites the Princess Theatre musicals of Bolton, Wodehouse, and Kern as the earliest examples of integration, this lineage goes back further—further than Hammerstein, further than Gershwin, further than Kern. To understand the history of the idea of “integration” in musical theatre, we must go back to the artist whose 1910 musical Madame Sherry, hailed as the “musical comedy rage of a generation,” was celebrated by critics for the way its “entertaining elements” were “cleverly interwoven into a consistent whole,” for the innovative ways that “the songs, lyrics, and ensemble numbers . . . are directly related to the story of the comedy, and there is a plausible excuse for every musical interruption.” That artist—who not only developed an innovative approach to musical theatre but also articulated a coherent theory of it—was Otto Harbach.