Important mediæval manuscripts and later literary and historical manuscripts, [12 cent, first ½]-[late 19 cent.], reflecting the collecting interests of the Maurice and Owen families of Clenennau and Brogyntyn.
They include an important mid-fifteenth century miscellany of prose and verse in Middle English (Brogyntyn MS II.1); English and Welsh poetry; plays; astrology and prophecies; chronicles of the history of Britain, one of which is a thirteenth century version of Historia Regum Britanniæ of Geoffrey of Monmouth (Brogyntyn MS I.7); a lute book, [c. 1595] (Brogyntyn MS I.27); a copy of the laws of Hywel Dda [1625x1632] (Brogyntyn MS I.12); legal precedents and other papers of legal interest in Latin and English; pedigrees, genealogy and heraldry of North and South Wales families; religious treatises, prayers, devotions and sermons; a seventeenth-century Latin-Welsh dictionary and other manuscripts of linguistic interest; extracts from classical literature; commonplace books; academic notes; copies of significant historical letters and documents; political tracts; moralistic and philosophical works; memoranda, journals and private papers of members of the Anwyl and Owen families; a few Brogyntyn estate and trust papers, 1727-1792; and notes on public offices and official papers deriving from the administration of Oswestry Corporation, 1660, 1673. Some ancilliary materials, [19 cent, second ½]-[1960s], mostly correspondence and notes relating to individual manuscripts, are also included (MSS I.27a, II.1a, II.10a, II.22a, II.42a, II.54(h), II.56a).

A collection of manuscripts, [12 cent.]-1909, from the library of Peniarth, Merionethshire, the core of the historic collection being that of the library accumulated at Hengwrt, Merionethshire, by Robert Vaughan during the seventeenth century. The collection includes many of the most important Welsh language manuscripts, including the Black Book of Carmarthen (Peniarth MS 1), the Book of Taliesin (Peniarth MS 2), the White Book of Rhydderch (Peniarth MSS 4-5) and Brut y Tywysogion (the Chronicle of the Princes) (Peniarth MS 20), as well as important manuscripts in other languages such as the Hengwrt Chaucer (Peniarth MS 392), the Law of Hywel Dda (Peniarth MS 28), Beunans Meriasek (Peniarth MS 105) and Bede's De natura rerum (Peniarth MS 540B).