Musical manuscripts and personal papers of William Mathias, including manuscript and published scores, 1950-1994; personal correspondence, 1972-1992; lectures and articles by him, 1972-1991; reviews, programmes, press releases, newsletters and ephemera relating to his work and honours awarded to him, 1952-1994; and correspondence of Yvonne Mathias relating mainly to performances of her husband's work, 1987-1994.

The five items deposited in 1995 was incorporated to the present structure and given E2d, B14c, K11b, K11c, and J1d as reference numbers.

Two items deposited in 1998 was incorporated to the present structure and given I1b and K18b as reference numbers.

Two items deposited in 2005 was incorporated to the present structure and given I27a and I28a as reference numbers.

An additional box of William Mathias's music manuscripts were received as a donation in August 2006. These manuscripts have been introduced at the end of the present structure as a Sub-fonds, entitled 2006 Donation, in February 2016.

William Mathias Recordings including reel to reel tapes, video tapes and vinyl records donated in July 2015 has been transferred to The National Screen and Sound Archive of Wales.