The Welsh collection is the Library’s main collection of Welsh and Welsh language books.

Within the Library this collection is known as Class X as the letter X always comes before the number on the shelf. This is also where books in the other Celtic languages are kept. A special effort is made to collect every Welsh publication throughout the whole world.

In addition to the British materials that come under the Copyright Act, the Library buys any works of Welsh interest published outside Wales. Every effort is also made to collect Welsh miscellaneous materials that are not included in the main stream from commercial publishers. The Library has a custodial responsibility to safeguard these smaller publications as well as more substantial books.