Ninety-four letters, 1919-1984, in Welsh and English, to Saunders Lewis from various correspondents, together with a few draft letters from Saunders Lewis and four letters to Margaret Lewis, written during her husband's imprisonment in 1937. Subjects discussed include Welsh nationalism, the award of DLitt honoris causa to Saunders Lewis, the Welsh Burial Grounds issue, 1928, and literary topics; enclosures include a copy of a draft constitution and articles of agreement, 1934, relating to self-government for Wales (ff. 161-95). Among the main correspondents are Edward Glyn Jones (13) 1919-28, Robert Williams Parry (14) 1927-44, John Arthur Price (5) 1928, E. Prosser Rhys (3) 1927-9, D. J. Williams, Fishguard (7) 1948-67, and Griffith John Williams (3) 1935-56.

The file is composed of electoral material and leaflets published by Plaid Cymru mainly during various general election campaigns between 1970 and 1992. Among them is a typescript copy of 'An Economic Plan for Wales' published by the party during 1970, and copies of 'Socialism and Nationalism in Wales' by Neil Evans, and 'Defeating Welsh Nationalism', November 1987, by Jon Vaughan Jones.