This is a study of the Mostyn family and estate down to 1642. The Mostyns were the result of a series of marriages in the fourteenth and fifteenth centuries which brought together the 'Five Courts' of Pengwem, Trecastell, Mostyn, Gloddaith and Tregamedd} these lines met in Richard ap Hyvel (d.1540) whose son Thomas first adopted the surname from his principal seat. The first part of the thesis deals with the history of the component families in the middle ages, while the second part covers the history of the Mostyn family from 1540 to 1642; it is followed by discussions of the estate and its management, of office, politics and public life, of litigation, of education and marriage and of the family as bardic patrons.
The Mostyns are of particular interest for several reasons. They were lucky; in every generation from before 1200 to 1831 they managed to produce a male heir and were therefore spared the rapid decline which failure brought to Gwydir for example. This also explains why they have retained so much of the original estate. They were never too ambitious; Richard ap Hywel's reputed refusal of Henry Tudor's invitation after Bosworth seems to symbolise their attitude. They played an active and important part in local government but they showed little enthusiasm for membership of parliament and they never sought to dominate their county. Their litigation did not reflect local rivalries; they seem, in fact, to have had few enemies. They gradually built up their estate and their fortunes, helped by the fact that they were among the first to exploit the coal measures on their lands on a commercial scale. And their role as patrons is highlighted by the part they played in connection with the two Caerwys eisteddfodau in 1523 and 1567.