The collection consists of the papers of Waldemar A. Nielsen from 1930-2004. The bulk of the collection dates from 1942 to 1998 and is organized into five series: World War II–Marshall Plan, Ford Foundation, African-American Institute–Iran, Consulting, and Publications.

The World War II–Marshall Plan series contains reports, correspondence, publications, and research materials used by Nielsen during his time working for the government during and after World War II. Of note are Nielsen's writings about public opinion polls and the bombing of Japan.

The Ford Foundation Series consists of three subseries: Correspondence, Reports, and the Reece Commission. Each subseries is arranged chronologically. Correspondence contains Nielsen's letters and memos while he worked for the Ford Foundation. Included in this subseries are several folders of Nielsen's daily memos from 1952 through 1961. Reports consists of office reports, president's reports, and research reports that Nielsen used or authored during his tenure at the Ford Foundation. The Reece Commission subseries contains materials related to the Reece Commission's investigation into the Ford Foundation in 1953 and 1954. This includes internal memos and notes by Nielsen and Ford Foundation President H. Rowan Gaither, Jr. as well as government documents and reports pertaining to the investigation.

The African-American Institute–Iran series contains Nielsen's correspondence, reports, and research materials from his tenure as the president of the African-American Institute as well as from his time working for the Empress of Iran. Of note are Nielsen's 1966 statement to the Subcommittee on Africa of the House Foreign Affairs Committee in which he discusses South Africa's policy of apartheid and Nielsen's report on philanthropy to the Empress of Iran.

The Consulting series contains Nielsen's correspondence, research files, and reports from his consulting agency, Waldemar A. Nielsen, Inc. Included in this series are subseries on his work with the Aspen Institute for Humanistic Studies (AIHS), the Buck Trust and Marin County Committee, and the Eugene Marion Kauffman Foundation. Of particular interest are the files related to Nielsen's involvement in the dispute and subsequent hearings over the intentions of the will of Beryl H. Buck.

The Publications series is divided into seven subseries based on Nielsen's articles, speeches, and individual published works. The Speeches subseries contains transcripts, drafts, research, notes, and correspondence from speeches Nielsen gave throughout his career. Articles includes research, correspondence, notes, and drafts of articles Nielsen wrote in a professional capacity as well as stories he had published in publications like The New York Times Magazine and The Saturday Evening Post. Subseries The Great Powers and Africa, The Big Foundations, The Endangered Sector, The Golden Donors, and Inside American Philanthropy all contain correspondence, notes, research materials, and drafts from the books Nielsen published over the course of his lifetime. In earlier documents in The Golden Donors subseries, Nielsen refers to the planned book as The Big Foundations II, before changing the title to The Golden Donors. In keeping with Nielsen's own labeling of his folders, individual folders of earlier materials relating to The Golden Donors are labeled as The Big Foundations II.