The collection consists of correspondence; manuscripts; case histories and records; organizational materials, including Youth Consultation Service, Children's Village, World Federation of Mental Health, American Mental Health Foundation, and Brooklyn State Hospital; video and sound recordings; awards and certificates; notebooks; book reviews; clippings; and notes from approximately 1905 through 1978. Materials document Slavson's career and offer an interesting look into the early days of group psychotherapy in New York City. There is considerable material on the Group Therapy Department of the Jewish Board of Guardians, psychotherapy in social service agencies, founding of the American Group Psychotherapy Association, as well as personal biographical materials. Among the collection were the papers of William Weinstone, founder of the Communist Party of the United States of America. Some of the early writings found in Series II may have been created by Weinstone and not Slavson.

The collection has been divided into seven series.

Series I: Correspondence and Biographical Material, 1917-1978, includes: general correspondence to and from Slavson from 1930-1978. The correspondence concerns books and papers written by Slavson, letters to editors, requests for information from social service agencies from around the world and letters to and from family members and friends. Also included are invitations to lecture, lecture schedules and biographical material, including: newspaper and magazine clippings and speeches from his retirement dinner at the Jewish Board of Guardians.

Series II: Published and Unpublished Manuscripts, 1900s-1970s. Slavson wrote approximately 200 articles and 16 books. This series includes published and unpublished manuscripts, some typed and others handwritten. Since most of the material was not dated, it is arranged alphabetically by title or topic (when no title was available). A great many (possibly) unpublished and undated material is present, including early writings consisting of poetry, novels, essays and short stories. The series begins with several folders of numbered articles which were intended to be published together in one volume. Boxes 6 and 7 contain journals and books, in English and other languages.

Series III: Group Treatment Records and Case Histories, 1927-1963. This series deals with treatment records and case histories and is closed to researchers.

Series IV-VII contain reprints of articles, clippings, photographs and audio and video recordings (unprocessed).