Of special interest in the Herbert A. Kellar Papers is the correspondence with historians, archivists, librarians, and agriculturists, filed under the headings of the various historical and library associations or the clubs of which Kellar was a member. (Note: Personal correspondence with historians, librarians, archivists, and agriculturists will be found in series 5: Historians and Agriculturists.)

These materials are varied as to quantity and quality, but in general they include correspondence, information in regard to programs and meetings, papers read, publications, committee reports, and Kellar's notes on these various functions of the organizations. As Kellar was a charter member, and often a founder of some of these groups, organizational information, rivalries among the groups, constitutional and membership data is informative. These are not official records, although there are some copies of official records, proceedings, and other publications of the various societies.

The historical associations (3.1) are arranged alphabetically. They include the Agricultural History Society (1919-1958); the Society of American Archivists (1934-1957); the American Association for State and Local History (1929-1954); the American Council of Learned Societies (1927-1956); the American Historical Association (1914-1953); the Business Historical Society (1930-1950); the Economic History Association (1940-1952); the Industrial History Society (1939-1940); the Conference of Historical Agency Executives (Midwest Historical Conference) (1935-1937); the Mississippi Valley Historical Association (Organization of American Historians) (1916-1957); the National Archives (1932-1953); and the Southern Historical Association (1935-1952). The subject files for the individual associations or organizations are chronologically ordered.

There is some material for over thirty other historically oriented organizations, committees, and conferences (3.2). This file is arranged alphabetically by name of organization, committee, club, or conference; and chronologically thereunder.

The library associations file (3.3) incorporates Kellar's collected materials pertaining to the American Library Association (1915 - [1934-1948]); the Association of College and Reference Libraries (1942-1948); the Special Libraries Association (1930-1949); the Experimental Division of Library Cooperation, the Library of Congress, of which Kellar was director in 1941-1942 (1896; 1902 - [1929-1962]); the Agricultural Library of the United States Department of Agriculture (1933); the Baker Library, Graduate School of Business Administration, Harvard University (1938-1951); the Chicago Metropolitan Library Council (1941-1946); Clements Library, University of Michigan (c. 1925-1946); the Council of Library Associations (1941-1942); the Huntington Library, San Marino, California (1948); the Illinois Library Association (1938-1948); the Illinois State Library (1947-1957); among others. The file is an alphabetical one; with a chronological treatment of the papers under each of the individual associations.