Deeds of the Aberpergwm estate in Glamorgan, Monmouthshire, Breconshire, and Carmarthenshire, 1258-1919; rentals and general account books of the estate (including some colliery accounts), 1791-1870, account books and balance sheets of the Aberpergwm colleries, 1794-1972; documents relating to Treferig Valley railway, 1874-1884; and personal papers, including letters to the Williams family of Aberpergwm and the associated families of Smith of Castellau, Llantrisant, Lloyd of Castellau and Aberpergwm and the Bush family of Burcot, Oxfordshire, 1760-1909; Castellau estate papers, 1867-1879; and papers, mainly 18th century, relating to the claims of inhabitants in the Forest of Dean.

Records of the Welsh estates of the dukes of Beaufort, earlier the earls of Worcester and William Herbert, earl of Pembroke (d. 1469), including records for the Breconshire lordships of Crickhowell, from 1382, and Tretower, from 1532; ministers' accounts for Monmouthshire lordships from 1387 and manorial records for the lordship of Chepstow, from 1568, Monmouth, from 1416, Porthgaseg, from 1262, Raglan, from 1364, Treleck, from 1508, and for the lordship of Usk, from 1517; records for the Seignory of Gower and Kilvey from 1366 and for the borough and manor of Swansea, 1657-1835; deeds from the 13th cent.relating to the Badminton estate in Monmouthshire, Breconshire and in Gower, Glamorganshire; records from the 16 cent. relating to the coal and iron industries in Monmouthshire and Glamorgan; and estate management records including rentals, 1638-1933, accounts of rent arrears, 1669-1839, bailiffs, collectors and stewards' accounts, 1652-1858, and registers of leases, 1629-1918.

Records mainly of the Glamorgan estate of the marquesses of Bute and of their predecessors, the earls of Pembroke. These include letters, 1588-1855, including letters of the Herbert family of Cogan Pill, 1588-1719, but primarily the personal and estate correspondence of John, second marquis of Bute, 1804-1855, (including letters relating to Bedfordshire, Cambridgeshire (Kirtling: Lady Bute's property) and County Durham estates); deeds, [1319]-1937; surveys, 1570-1842; rentals of the Glamorgan estate, 1728-1893, and the Cardiff estate, 1842-1895, estate and manorial accounts, 1573-1873; manorial records and deeds of over seventy manors, mainly in Glamorgan, [?1373]-1847; family settlements, [early 17 cent.]-1902; family probate records, 1612-1900; and legal and case papers, 1642-1921; correspondence of Alice, Lady Windsor, 1757-1776; a substantial number of copies of Acts of Parliament, relating mainly to roads, canals, docks and harbours, railways, public works and utilities, 1771-1928; and miscellaneous records. -- The archive illustrates the history of Glamorgan; the corporate life of the boroughs of Cardiff, Cowbridge and Llantrisant; the urbanization of the South Wales valleys, especially Merthyr Tydfil and Aberdare; the Glamorgan Commission of the Peace; the county militia and yeomanry, 1815-1837; the development of the coal and other industries (it includes papers relating to minerals and ironworks 16th-early 20th cent., accounts of coal shipped from Neath, etc. 1626-1682, quarry and lime kiln accounts 19th cent. Cardiff railway, dock and harbour papers and plans, 19th-20th cent.); labour and political unrest, including Chartism, Scotch Cattle, Rebecca riots; early trade unions; and the history of Cardiff castle, 16th-19th cent., including inventories 1581, 1585, estimate of repairs 1590 and plans of grounds.