The Leonard J. Arrington Papers are divided into 13 different series which reflect his personal life, his professional career, and his research interests. The first five series deal with his professional life, both as an educator and as Church Historian for the Church of Jesus Christ of Latter-day Saints from 1972 to 1982. The first series consists of his teaching files and the research projects he conducted while a professor at Utah State University and Brigham Young University. The next two series deal specifically with his tenure as Church Historian, with one series containing his correspondence as Church Historian and the other documenting the work conducted by his staff and himself. The fourth series consists of records of his affiliations with professional organizations such as the Mormon History Association, the Utah State Historical Society, the Western History Association, and others. This series contains newsletters from the associations, correspondence with members, and documents concerning events such as the founding of the Mormon History Association and the establishment of the Western Historical Quarterly. The fifth series contains correspondence with and files about scholars, associates, and colleagues.

The next four series document Arrington's research interests. One series contains his files on women's history; another his research on Utah history; a third his work on the Great Depression and the New Deal; and a fourth his research files in Mormon history. This last group is especially important, as it contains both primary documents and secondary material. The primary documents consist of such items as minutes of the LDS Church's Quorum of the Twelve Apostles, Brigham Young's letter books, and diaries and journals from high church leaders such as Heber C. Kimball and Willard Richards and from everyday saints such as Richard Roskelley. The secondary material consists of extensive research files on a variety of topics, including the LDS Church and African Americans; the Equal Rights Amendment and the Mormons in the 1970s; and LDS Church Presidents, as well as biographies of numerous Mormons, files on authors who wrote about Mormonism, research on the Mormon Church's business enterprises, and drafts of articles, books, dissertations, and theses on Mormonism. This series ends with Arrington's extensive newspaper clippings on the LDS Church from the 1940s to 1997.

The next two series illuminate Arrington's personal life. Series ten consists of his personal papers, including correspondence, New Year's Resolutions, speeches given in junior high school and high school, drafts of autobiographies and memoirs, scrapbooks, documents about his military service, his files of newspaper and magazine clippings, his exams from the University of Idaho, his class notes from the University of North Carolina, and his extensive diary which runs from the 1930s to 1998. Series eleven consists of his family papers, including information about his wives, children, parents, and brothers and sisters, as well as his family history.

The last series in the Arrington collection consists of his writings. This contains drafts and notes of almost all of Arrington's writings, including Great Basin Kingdom (1958); a history of First Security Bank (1973); Beet Sugar in the West: A History of the Utah-Idaho Sugar Company (1966); The Mormon Experience (1979); Brigham Young: American Moses (1985); History of Idaho (1994); Adventures of a Church Historian (1998); and an unpublished biography of W.W. Clyde. The collection also holds over one hundred articles and speeches that Arrington wrote or gave.

The materials in Series 13 were donated to USU Special Collections in 2006 by Susan Arrington Madsen, the daughter of Leonard J. Arrington. This sixty-five box addendum consists of Leonard J. Arrington's working files and contains his correspondence, research papers, speeches, and other similar materials. These papers span the period of 1938 to 2013 with the bulk spanning 1965 to 1997. The correspondence in this series concerns Arrington's dialogue with various Mormon history scholars, his work as Church Historian, and with various organizations. Box 64 contains research papers used to formulate The Mormon Experience and were complied and donated to USU Special Collections in 2003 by Richard Daines.

Because of Arrington's prolific career, the Leonard J. Arrington Papers provides an abundance of material about Mormon history and the history of the American West. In general it is an important resource for scholars interested in Mormon history topics. Perhaps the primary importance of the collection, however, is its documentation of the Mormon history field in the late twentieth century, a time when the discipline truly came into its own. Fifty years from now, scholars will be able to piece together why such an abundance of scholarly Mormon history was produced during this era, in large part because of the records and documents that Arrington left behind. His Church History Division files, his drafts of his own writings, his personal papers, and his files on his professional affiliations all help to tell the story of Mormon historiography. Whether one is interested in Mormon history in general, or merely in the life of one of the most prolific and outstanding scholars of American history, Leonard J. Arrington's papers provide an abundance of information.

In addition to this manuscript collection, a separate photograph collection has been created containing photographs that were donated with Arrington's papers. For preservation purposes, all intact newspapers have also been removed from this collection and replaced with a reference note.