The collection contains personal and legal correspondence; legal documents pertaining both to cases handled by Abraham Unger and those of interest to him; published and unpublished writings; records of the National Lawyers Guild and of its New York City chapter; subject files; and clippings and printed ephemera.

Notable correspondents include lawyers Bella Abzug, Ben Margolin and Samuel Rosewein. Notable clients represented (usually as defendants) include: The American Communications Association, attorney Maurice Braverman and Abraham Isserman (contempt / disbarment in connection with Smith Act case activity); the Communist Party state organizations of Alabama, Colorado, Georgia, Louisiana, New York, Ohio, Pennsylvania, Texas, Virginia, and Washington; Gerhart Eisler (passport and deportation); and (on behalf of Curran), Andrew Furuseth, President of International Seamen's Union of America v. Joseph Curran, Joseph, Chairman Provisional Strike Committee (1936), Willie McGee, and Unger's son Nicholas. The National Lawyers Guild series includes correspondence of Unger and other members, minutes of the executive board and of several committees, including that overseeing the publication of the Lawyers Guild Review, convention materials, and statements and resolutions and other internal documents. The NLG New York City Chapter series contains executive board minutes and correspondence, files on New York State court reform, committee and general records, membership lists, and resolutions and statements.

The Subject Files series covers numerous organizations, causes, events, and some individuals, with an overall focus on civil rights and liberties and laws and legislation. Files include: the American Bar Association, American Birobidjan Committee, Anti Red Ordinance (Birmingham, AL), Ben Davis Bail Committee, Oscar Collazo (Puerto Rican nationalist), the Columbia University Student Strike of 1968, the Committee to abolish HUAC (U.S. House Committee on Unh-American Activities), Council on African Affairs, Emergency Civil Liberties Committee, Bill Eption (Puerto Rican nationalist), International Labor Defense, Lawyers Committee to End the War in Vietnam, the New York State's 1949 "Feinberg" law (providing for the dismissal of teachers belonging to "subversive" organizations), and the Trade Union Committee to Defend Louis Weinstock.

Materials added to the collection in 2016 predominantly include documents related to Unger's legal defense of members of the Puerto Rican Independence Movement. They include Unger's notes and legal documents related to the cases of Oscar Collazo and Juan Bernardo Lebron, both of whom he defended in the 1950s. The accretion also contains clippings, ephemera, and articles related to the Puerto Rican Independence Movement and its leader Pedro Albizu Campos. Other materials in this accretion include Unger's personal correspondence between 1947 and 1952 and papers related to Unger's involvement in the Communist Party of the United States.