Correspondence and papers, 1842-c. 1955, of poet and socialist Robert Jones Derfel and including letters and cards, c. 1852-1905, from various correspondents; poetry and sermons, 1842-1913; scrapbooks, 1855-1905, containing material relating to Welsh socialism, etc.; books and pamphlets; and research material, 1911-c. 1955, compiled by T. J. Roberts in the course of his study of Robert Jones Derfel.

Administrative papers of Plaid Cymru National Left/Chwith Genedlaethol including agendas, minutes, motions, correspondence, along with publications discussion papers.

Correspondence of David Thomas, 1907-1929, together with pamphlets, reports and other printed items relating mainly to socialism, the Independent Labour Party, workers' unions, agricultural wages, publication of Y Werin a'i Theyrnas, local committees in North Wales for improvement of social conditions, the Caernarfonshire parliamentary election, 1922, and miscellaneous unspecified subjects; incomplete copies of David Thomas's printed works, articles and parts of his thesis, 1928; account books, [c. 1878]-1910, belonging chiefly to John Williams, Bwlchgwyn, Denbighshire; a small notebook containing literary adjudications in connection with an eisteddfod at Tal-y-sarn, 1908, and translations of six stories from French into Welsh by Morfudd' [Miss H. Jones, Porth] andNehushtan' [N. El. Thomas, Swansea], entered at the Barry National Eisteddfod 1920.

A draft of 'Y Blaid Genedlaethol a Marxiaeth', an address by Saunders Lewis to the Caernarfonshire Conference of the Welsh Nationalist Party, 26 February 1938; and other miscellaneous papers, 1922-89.

Welsh Republican Movement and Plaid Cymru papers collected by Cliff Bere, 1940-1973, including correspondence, [c. 1947]-1965; membership forms and subscriptions, [c. 1948]-1957; constitution, meetings and reports, 1949-1952; newspaper cuttings, 1949-1991; political and personal correspondence, 1933-1997; papers relating to Plaid Cymru, [c. 1949]-1996, including the Parliament for Wales Campaign, Cymdeithas yr Iaith (Welsh Language Society) campaign for bilingual road signs, 1971; 'Cofiwn', the National Commemoration Association, 1976-1987; the Welsh Socialist Republican Movement (Mudiad Gweriniaethol Sosialaidd Cymru) 1975-1985; Cymdeithas Cyfamod y Cymry Rhydd (the Society of the Covenant of the Free Welsh) 1986-1994; Cardiff City Planning Department, 1965-1982; Harri Webb papers, 1949-1996; Eurig ap Gwilym [d. 1988], 1976-1988; papers relating to holiday homes arson campaign and Bere's arrest, 1980-1982; Yr Undeb Celtaidd /The Celtic League, 1988-1993; the Free Wales Army, 1993-1998; unpublished drafts of articles, 1934-1996; various journals and pamphlets, [c. 1946]-1976; newspapers cuttings, 1946-1997; undated translations of pamphlets published by the National Museum of Wales; papers, 1984-1998, relating to his publications, and other printed ephemera, 1935-1956.

Papers relating to fringe Nationalist and left wing groups, 1963-1989, including material relating to Welsh Nationalist and Republican Groups, 1963-1989, material relating to Welsh left wing groups, 1969-1979, and papers relating to solidarity groups and campaigns, 1968-1989; published political material such as newspapers and periodicals, 1913-1989, records and papers of Cofiwn, 1970-1990, including material relating to the American Indian Movement Tour of Wales, 1986; papers relating to campaigns and activities of groups such as the the Owain Glyndwr Society, 1975-1990; papers relating to maritime history and heritage, 1973-1995; and miscellaneous papers, mainly relating to organisations in Aberystwyth, 1976-1989.