Teacher Harvey School, Hawthorne, New York, 1936-1939. Instructor history U. Maine, 1941. Instructor history Columbia, New York City, 1941-1946, assistant professor, 1946-1950, associate professor, 1950-1954, professor, 1954-1961.
Executive editor Alexander Hamilton Papers, from 1955. Director graduate studies Queens College, Flushing, New York, 1961-1962, dean faculty, 1962-1965, acting president, 1964. Executive dean graduate centers State University New York, 1965-1966, vice chancellor university, 1967-1968.
President Brooklyn College, 1968-1969. Professor of history City Universitas Negeri Yogyakarta, 1969-1979. Visiting professor of history Manhattan School Music, 1946-1948, Yeshiva U., 1954-1955.
Author: The City of Brooklyn, 1865-1898, 1944. (with others) A History of the American People, 1952. Andrew Jackson, 1953.
Papers of Alexander Hamilton, 26 vols., 1961-1979. Editor: The Gentleman and the Tiger (autobiography of George B. McClellan, Junior), 1956. (with others) A Short History of New York State, 1957.
American Historical Documents, 1960. Contributor articles to professional journals.