One fundamental difference between Wales and England is the use of patronymics in Wales as opposed to fixed surnames in England. Examples of this system are Griffith Lewis, son of Lewis John William, and Harry David, son of David John Rees, both witnesses to a grant of properties in the parish of Llandeilo Fawr, Carmarthenshire, in 1683. Similarly, the marriages of Thomas Morris and Elizabeth Morris, spinster, the son and daughter of Morris Thomas, farmer, are recorded in the parish register of Llansilin, Denbighshire, exactly a century later. In its earlier form, the naming system usually included ab or ap (meaning son of) or ferch (often written verch, meaning daughter of) e.g. the baptism of Elin verch William ap Llywelyn in Llandegfan, co. Anglesey, in 1599.

From the 16th century onwards, the Welsh gradually adopted the English system, the change occurring sooner in the higher strata of society and near the English border than among the common people of the western areas where the process was still incomplete in the early 19th century.

One evident result of this gradual development is the lack of variety of surnames in many parts of Wales, whereas, in the border counties, venerable Welsh names such as Llywarch survive as surnames to this day. Another is the existence of many Welsh surnames beginning with P or B: Bowen (from 'ab Owen'); Beynon (from 'ab Eynon'); Powell (from 'ap Howell'); and Prytherch and Prothero (from 'ap Rhydderch'). Married women were also frequently referred to by their maiden names, e.g. Jennett Bennett, wife of David Thomas Rees Prees, in the grant of 1683 previously mentioned, and Margaret Roberts, wife of Evan John, in the parish register of Llangybi, Caernarfonshire, in 1749.

For a fuller discussion of patronymics and surnames see T J Morgan and Prys Morgan, Welsh Surnames (Cardiff: University of Wales Press, 1985), and John and Sheila Rowlands, The Surnames of Wales (Federation of Family History Societies Ltd, 1996).