The Library has substantial holdings of early printed material in Welsh, English and other European languages, ranging from the 15th to the early 19th century. There are also substantial holdings of publications of modern private presses, including a comprehensive collection of the works of the Gregynog Press. Some of the Library's early printed books are kept as separate collections, while others form part of the main collection. Some of the rare books have not yet been added to the online catalogue, and readers are advised to check the microfiche catalogues in the reading rooms for older books which do not appear in the online catalogue. Typed schedules of a number of these collections are available in the North Reading Room.
Libri Walliae: a catalogue of Welsh books and books printed in Wales 1546-1820 was published by the Library in 1987. A supplement was published in 2001. Copies are available in the reading rooms.
Two foundation collections form the basis of the Library's holdings of rare books:
• The Sir John Williams Collection (see separate article)
• The University College of Wales Collection: The Welsh Library at the University College of Wales, Aberystwyth was transferred to the National Library in 1909. It contains about 13,400 volumes, including the libraries of the 19th-century collectors the Rev. Owen Jones, Llansantffraid and Richard Williams of Celynog, Newtown. The collection is strong in 19th-century Welsh theological works, 18th-century Welsh classics and collections of hymns.
The libraries of two of Wales's cathedrals are held at the National Library:
• Llandaff Cathedral Library: The more valuable and rare printed books from the Cathedral Library were deposited at the National Library in 1943 and purchased by the Library in 1984. The collection contains about 800 items in 200 volumes, mainly theological in content, including numerous volumes of 17th- and 18th-century sermons.
• St. Asaph Cathedral Library: This library remains the property of the Cathedral, but has been on permanent deposit at the National Library since 1970. It consists of about 2,500 volumes.
A number of country house libraries have been acquired by the National Library over the years. In some cases these include both manuscripts (see separate article) and printed books. These collections include:
• Castell Gorfod: The library of Captain James Buckley of Castell Gorfod, St. Clears, Carmarthenshire, including the library collected by his maternal grandfather, Joseph Joseph, F.S.A., of Brecon. It contains 1,500 items on history, genealogy and topography, in particular material relating to the counties of Brecknock and Carmarthen, in both English and Welsh.
• Chirk Castle: A collection of about 350 volumes and about 500 pamphlets from the library of the Myddelton family of Chirk Castle near Wrexham. The remainder of the library was recently purchased by the National Trust and is kept at the castle.
• Dolaucothi: A collection of about 1,400 volumes from the library of the Lloyd-Johnes family of Dolaucothi, Carmarthenshire, containing 18th- and 19th-century publications, including a significant number of items on India and the colonies.
• Plas Power: A collection of about 220 volumes from the library of Plas Power near Wrexham.
The Library has over the years acquired the collections of a number of individuals, in addition to the foundation collection of Sir John Williams:
• Anderson: A collection of about 140 works by or relating to John Donne, purchased from the executors of R.A. Anderson of Llantwit Major, Glamorgan.
• Bourdillon: The collection of Francis William Bourdillon of Midhurst, Sussex contains 150 manuscripts and 6,178 printed volumes, including 66 of the Library’s 250 incunabula (books printed in the 15th century). The collection is rich in French mediaeval literary texts and studies and early illustrated books. It includes 23 editions of the Roman de la Rose printed before 1550.
• Lewis Weston Dillwyn: A collection of about 1,000 volumes from the library of the botanist L.W. Dillwyn, illustrating the development of botany from the 16th to the 19th century.
• Henry Hey Knight: A collection of about 3,000 volumes of philosophy, theology, history, topography and English and classical literature, from the 16th to 18th centuries.
Perhaps one of the more unexpected collections found in the National Library of Wales is the collection of editions of Euclid’s Elements and other works ascribed to him. The basis of the collection is 39 volumes donated by Sir Charles Thomas-Stanford, but the Library has continued to add to the collection, which now contains over 300 volumes.
The Library continues to acquire rare books by purchase, donation and bequest. The aim is to obtain works in the Welsh language, written by Welsh authors, printed in Wales or relating to Wales and the Welsh, as well as copies of books which have belonged to notable Welsh individuals. Efforts are also made to add to those subject areas in which the Library already has significant holdings.