Cofnodion Plaid Cymru, 1915-1999, yn cynnwys cofnodion, agenda and gohebiaeth y pwyllgor gwaith a phwyllgorau eraill, 1925-1997; gohebiaeth gyffredinol, 1925-1998, gyda nifer o aelodau a swyddogion blaenllaw y blaid; cofnodion, gohebiaeth a phapurau eraill y gwahanol bwyllgorau rhanbarthol, 1925-1997, a changhennau,1930-1992; cofnodion a dogfennaeth y Cyngor Cenedlaethol, 1967-1997; cofnodion ariannol, yn cynnwys rhai papur newydd misol y blaid Y Ddraig Goch a Welsh Nation a Chronfa Gŵyl Ddewi, 1927-1996; rhaglenni a threfniadau ar gyfer cynadleddau ac Ysgolion Haf, 1933-1998; cofnodion aelodaeth, 1930-1996; papurau y Grŵp Ymchwil, [c.1960]-1995; papurau, yn cynnwys areithiau ac effemera, yn ymwneud ag etholiadau, 1929-1999; papurau yn ymwneud ag Adran y Menywod, 1924-1996, a'r Mudiad Ieuenctid, 1964-1998; papurau yn ymwneud â refferendwm datganoli 1979,1969-1983, a refferendwm 1997, a Chynulliad Cymru,1992-1998; papurau yn ymwneud â Y Ddraig Goch, Welsh Nation a chyhoeddiadau eraill, 1932-1996; deunydd printiedig gan Blaid Cymru ac eraill yn cynnwys llyfrau, cyfnodolion a phamffledi,1913-1996; torion o'r wasg, 1924-1996; cylchlythyron, 1938-1992; papurau yn ymwneud â'r Blaid Seneddol,1980-1996; papurau unigolion ac rhai ar wahanol bynciau amrywiol, 1926-1998 = Records of Plaid Cymru, 1915-1999, including minutes, agendas and correspondence of the executive and other committees, 1925-1997; general correspondence, 1925-1998, with many prominent party members and officials; minutes, correspondence and other papers of the various regional committees, 1925-1997, and branches, 1930-1992; minutes and records of the National Council, 1967-1997; financial records, including those of the party's monthly newspaper Y Ddraig Goch and Welsh Nation and Cronfa Gwyl Dewi, 1927-1996; arrangements for and programmes of conferences and Summer Schools, 1933-1998; membership records, 1930-1996; papers of the Grŵp Ymchwil (research group), [c.1960]-1995; papers, including speeches and ephemera, relating to elections, 1929-1999; papers relating to the Adran Menywod (Women's Section), 1934-1996, and the Mudiad Ieuenctid (Youth Movement), 1964-1998; papers relating to the 1979 devolution referendum, 1969-1983, and the 1997 referendum and Welsh Assembly, 1992-1998; papers relating to Y Ddraig Goch, Welsh Nation and other publications, 1932-1996; printed matter by Plaid Cymru and others including books, periodicals and pamphlets, 1913-1996; press cuttings, 1924-1996; circulars, 1938-1992; papers relating to the Parliamentary Party, 1980-1996; papers of individuals and to various miscellaneous topics, 1926-1998.