When one considers how intimately the ecclesiastical history of Wales has been bound up with that of England from at least the twelfth century until the disestablishment of the Welsh church in 1920, it is perhaps surprising that the subject should present as many problems as it does to those approaching it for the first time, especially to those familiar with the sources of English ecclesiastical history. It will not, of course, be possible in a paper of this length to consider fully all the problems involved, and I wish therefore to confine myself to four which seem to me to be absolutely basic. They are the shortage of primary source material; the lack of competent monographs on many topics; the language barrier which faces those unfamiliar with Welsh; and the dangers inherent in what may be called the ‘Welsh Nationalist’ approach to Welsh ecclesiastical history.