The Peg Mullen papers measure 5.25 linear feet and date from 1966 to 2010. The bulk of the collection consists of correspondence and newspaper clippings from the 1970s related to the anti-warmovement. The papers are arranged in five series: Biographical information, Correspondence, Friendly Fire, Vietnam War resource files, and Unfriendly Fire: A Mother's Memoir.

The Biographical information series (1970-2010) includes newspaper clippings, articles, and interviews with Mullen from the 1970s through 2003; most of these materials describe Mullen's activism against the war in Vietnam, but a few are related to the Persian Gulf War and the Iraq War. Newspaper articles about Michael Mullen and the circumstances of his death in Vietnam are included in this series as well as letters written by Michael Mullen from Vietnam to his parents. A history of the Mullen family, "Six Generations in Black Hawk County, 1852-1996," and a short sketch of her father written by Peg Mullen. Four interviews with Mullen conducted in the 1990s, newsletters carrying columns written by Peg Mullen, and several photographs of Peg Mullen, and of her son, Michael, complete the series.

The Correspondence series (1968-2003) consists primarily of letters written to the Mullens during the 1970s, and especially from the periods immediately following Michael Mullen's death in 1970, the publication of Friendly Fire in 1976, and the television adaptation of the book in 1979. It includes contacts with the White House, the Pentagon, political leaders, and letters from hundreds of Americans expressing support for the Mullens. The series also includes correspondence between the Mullens and the Pentagon pertaining to the Mullens' quest to determine the cause of their son's death. Carbon copies of many of the outgoing letters are included with the responses. (Many additional letters from this period can be found in the series, Unfriendly Fire: A Mother's Memoir.) The series also includes letters from the 1990s relating to the US wars in the Persian Gulf and Iraq, and correspondence between Mullen and high school students from Mt. Pleasant, Iowa. Mullen continued to receive letters from Vietnam veterans in the 1990s.

The Friendly Fire series includes the portions of C.D.B. Bryan's book, Friendly Fire, which first appeared in The New Yorker magazine and correspondence from 1971 to 1979 between Mullen and Bryan. Also in this series are a typescript of the book, published in 1976; Fay Kanin's script for the television adaptation; a VHS copy of the film, Friendly Fire, and a bound notebook of articles concerning popular response and television critics' views.

The Vietnam War resource files (1966-1978) include anti-war correspondence, draft resistance materials, petitions, newspaper clippings, reports, speeches, and memoranda gathered by Mullen during the 1970s. The series contains a "Vietnam Information Packet," which was compiled bymembers of Milestones, an independent high school newspaper. This series includes information from six organizations that Mullen belonged to: American Friends Service Committee, Another Mother for Peace, Business Executives Move for Vietnam Peace (BEM), Common Cause, SANE, and Women's International League for Peace and Freedom (WILPF). Other causes Mullen supported include National Strike for Peace, the abolition of the draft, and Four folders of letters and one folder of postcards written by persons in support of Amendment 609 complete the series.

The Unfriendly Fire: A Mother's Memoir series (1970-1996) includes four drafts of the manuscript. Also included is correspondence datingfrom the 1970s to and 1990s that Mullen used while writing the memoir. Part of the correspondence is organized topically, the remainder chronologically. The newspaper clippings pertain to the Vietnam War, especially casualty notices. Materials relating to the publication and response to the book complete the series.