During Fritz Reiner’s forty-year conducting career in the United States, he championed Béla Bartók’s orchestral music, programming Bartók’s orchestral works on over sixty concerts with the Cincinnati Symphony Orchestra, Pittsburgh Symphony Orchestra, Chicago Symphony Orchestra, and with other major American orchestras. These included performances in which the composer himself appeared as a soloist. Moreover, Reiner continued to conduct Bartók’s music following the composer’s death, and his efforts to promote Bartók’s works contributed to their significance to the American orchestral repertoire. The thesis explores connections between performance markings in Reiner’s personal copies of Bartók scores and the recordings he made of them, the ways in which Reiner’s live performances and recordings of Bartók’s music affected the American reception of Bartók’s works, and how Reiner’s collaboration with Bartók related to the revision of Bartók’s orchestral works in their published forms through case studies of Bartók’s Piano Concerto no. 1, Concerto for Orchestra, and The Miraculous Mandarin. The first case study considers Bartók’s performances of his Piano Concerto no. 1 with Reiner during his first U.S. concert tour of 1927-1928. Following an overview of Bartók’s activities in America during that time, three first-edition scores of Piano Concerto no. 1 are analyzed in order to show the significance of handwritten additions, corrections, and conducting markings made by Fritz Reiner, a Universal Edition staff member, and Serge Koussevitzky in preparation for performances with Bartók in 1928. It not only provides a window into early performances of the work with the composer at the piano in the absence of a recording, but also offers insight into Bartók’s preferences for performance of the work, some of which are reflected in the first or second editions of the work, and some of which are only preserved in Reiner’s scores. The second case study examines a new source for Bartók’s Concerto for Orchestra held at Northwestern University that bears extensive corrections by Bartók, as well as Reiner’s conducting markings. It discusses the circumstances surrounding Reiner’s acquisition of the score and its role in Reiner’s performances and recordings of Concerto for Orchestra with the Pittsburgh Symphony Orchestra and the Chicago Symphony Orchestra. The third and final case study details Reiner’s preparation and performance of two concert versions (“Scenes” and “Suite”) of Bartók’s pantomime The Miraculous Mandarin using Reiner’s annotations to four versions of the score held at Northwestern, Bartók’s correspondence with his publisher, and program notes from Reiner’s 1927 world premiere of the “Scenes” to provide a better understanding of Reiner’s preparation and performances of both the “Scenes” and “Suite.” It further analyzes press coverage of his performances of the “Suite” to demonstrate that the press reaction to objectionable elements of the plot mellowed over time, and that critics consistently praised Reiner’s expert preparation and interpretation of the work. The thesis considers the publication and performance history of Bartók’s Piano Concerto no. 1, Concerto for Orchestra, and the concert versions of The Miraculous Mandarin in terms of Reiner’s collaboration with Bartók, his role in the promotion of Bartók’s music in the U.S., and his reputation as an authoritative interpreter of it.