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).

A vellum manuscript with illuminated capitals comprising an incomplete transcript of the 'Divinae Institutiones' of Lucius Caelius Firmianus Lactantius.

A manuscript containing scholastic tracts including disputations on Aristotle's 'De Anima' said to have been collected by Master Benedict and pronounced by the Master Regent of 'Fragfordie' [sic] in 1418; treatises on 'ars algoristica', physiology, and astronomy; 'liber de causis', probably the work of David Iudaeus [David ben Yom Tov]; 'comptus norembergensis'; and fragments of other texts, including a sheet containing verses beginning 'lumina lauas surgens gelida manus vnda' (cf. Schola Salerni).

A manuscript containing four folios from a fourteenth-century illuminated manuscript relating to scriptural and other eastern genealogies; the emblazoned pedigree of Thomas Williams by Griffith Hughes, 1638; and fragments of pedigree tables of the Salusbury, Grosvenor, Davenport, Egerton and other families.

Incomplete versions of 'Le Romans de Charité' and the 'Miserere' of the Renclus [i.e., recluse] de Moiliens.

A manuscript copy, with illumination, of the 'Roman de la Rose' of Guillaume de Lorris and Jean de Meung.

A manuscript copy of the 'Roman de la Rose' of Guillaume de Lorris and Jean de Meung.

An incomplete manuscript of 'Li Livres des Estoires dou Comencement dou monde', belonging to the 'Premiere Redaction', but not followed by the 'Faits des Romaine'.

A transcript of the metrical version by Couldrette (Coudrette) of the romance of Mélusine.

A manuscript containing expositions of the canon of the Mass by Pope Innocent III, Odo, bishop of Cambrai, 1105-1113, Richard of Wedinghausen, and others.