Papers of Sir Idris Foster comprising correspondence; personal papers, 1953-1978; papers, 1963-1978, relating to the Standing Commission on Museums and Galleries; radio and television scripts, [1949x1984]; notes and correspondence relating to his work on `Culhwch ac Olwen', including copies of his MA thesis, 1935-1961; scholarly and academic notes; papers relating to the National Eisteddfod, 1960-1985; material on Ireland and the Irish language, 1958-1982; copies of university dissertations, 1924-[1980]; drafts and typescript versions of articles, lectures and broadcasts received by Foster, 1949-1983; and index slips of Old and Middle Irish and Middle Welsh words; papers relating to the Honourable Society of Cymmrodorion, 1947-1978, the University of Wales, 1936-1984, including the Board of Celtic Studies,1955-1975; Jesus College and Oxford University, 1960-1984, the Church in Wales, 1957-1983, archaeological bodies, the Ancient Monuments Board for England and Ancient Monuments Board for Wales, 1960-1985, the National Eisteddfod, 1960-1985, Cyngor yr Iaith Gymraeg, 1973-1977, and other councils, committees and societies, 1951-1984.

Three copybooks of lecture notes, 1902-1904, compiled by John Tudor of Hebron, Pembrokeshire, whilst an undergraduate at the University College of North Wales, Bangor.
The volumes include notes on Welsh poetry (1450-1600) and exercises in Hebrew grammar (NLW MS 16192iB); notes on Welsh poetry (1300-1450), notes on Welsh and Irish philology and a comparative list of Irish and Welsh words (NLW MS 16192iiB); and notes on Welsh poets of the fifteenth century (NLW MS 16192iiiB). A note from the donor is included (with NLW MS 16192iB)

Manuscripts, [late 12 cent.]-[early 20 cent.], formerly part of the library of the Mostyn family of Mostyn Hall, Flintshire, comprising transcripts and extracts from Giraldus Cambrensis, Geoffrey of Monmouth, Dares Phrygius, Nennius, Gildas, David Jenkins (Judge Jenkins), Sir John Wynn of Gwydir, Lydgate's 'Life of Our Lady', Leland's Itinerary, 'Chroniques de France', historical manuscripts such as Brut y Tywysiogion and Brut y Brenhinoedd, Welsh romances and the Mabinogion; collections of mainly Welsh poetry, among them the seventeenth-century volumes Llyfr Coch Nannau and Llyfr Gwyn Corsygedol, containing poems by Dafydd ap Gwilym, Guto'r Glyn, Tudur Aled, Siôn Cent and others; genealogies, pedigrees and histories; official papers relating to Caernarvonshire; catalogues of the Mostyn and Gloddaeth libraries, 1692-1842; etc.

A scrap book compiled by John Jones ('Myrddin Fardd') containing manuscript notes and press cuttings on Welsh orthography, the significance of the poetry of mediaeval Welsh bards, etc. ('Orgraff', 'Geiriau', 'Yr Iaith yn Newid', 'Gweithiau y Beirdd', 'Canu Clod eu Noddwyr', etc.).

Letter, 13 October 1982, from Saunders Lewis, Penarth, to Kathryn A. Klar, Richmond, California, replying to a letter concerning her research into Canu Aneirin at the University of California, Berkeley.
He describes the negative reaction of Ifor Williams, amongst others, to his book Braslun o Hanes Llenyddiaeth Gymraeg (Cardiff, 1932), the conclusions of which however correspond with those of Klar and her colleagues; he also describes his current state of health.