The collection consist of Marshak's professional and personal papers, detailing his career as university professor in physics at the University of Rochester and Virginia Tech, member and leader in several scientific institutions, and president of the City College of New York.

The first series contains materials on the Shelter Island Conferences (1947-1949) and his administrative and correspondence files on the Rochester Conferences on High-Energy Physics (1950-1957), which he founded. After 1957 the conferences were held under the sponsorship of the International Union of Pure and Applied Physics (IUPAP) and Marshak's files from the conferences from 1958 to 1970 are included. The collection also has correspondence files on IUPAP (1953-1972) and on the Commission on High Energy Physics (1958-1963); photographs (1950-1970); US-USSR relations (1956-1966); and a photocopy of an oral history interview done by Charles Weiner (1970).

The rest of the collection, is divided into eight series. These series consist of correspondence, notes, reports, files, speeches, newsclippings, autographs, photographs, transcripts, proceedings, interviews, and other personalia. Topics cover the national and international development of high-energy physics, meetings and symposia, and scientific committees; awards and prizes, administration and education, science in the Eastern Bloc and Third World, and the scientist as social activist or citizen-scientist. The collection also includes correspondence, publications and articles, and more related to Marshak's books and other writings, teaching and academic administrative work, and research.

Individual series concern specific time periods of Marshak's career, including his work at the University of Rochester, City College of New York (CCNY), and Virginia Tech (VPI). The series also document his involvement in numerous organizations, including the American Physical Association, International Center of Theoretical Physics in Trieste, Italy, and the International Foundation for Science in Sweden. (However, Marshak's official records as president of City College of New York are held by the Hoover Insitution Archives at Stanford University.)

Of special note are several items and files with other well-known physicists, including Hans Bethe, George Sudarshan, J. Robert Oppenheimer, Susumu Okubo, Abdus Salam, Victor Weisskopf, Enrico Fermi, Isidor Isaac Rabi, Mildred Dresselhaus, Richard Feynman, and a letter from Albert Einstein.