My dissertation is a palaeographical study of the manuscripts of the works of Gerald of Wales (c. 1146-1223). Gerald was a churchman, a member of the court of King Henry II and a prolific author. His extensive works include historical and topographical descriptions of Ireland and Wales, theological and hagiographical studies, and several autobiographical works. Throughout his career he constantly revised these works. A hundred manuscripts containing works of Gerald survive today, and the progress of his revision of his works may be observed from the manuscript-record. I therefore devote some space to the textual history of Gerald's works in the manuscripts; however, the emphasis is on the manuscripts and therefore on what the textual history can show about them, not on the texts themselves. There is an unusually large number of manuscripts (about 20%) surviving from Gerald's lifetime, including some which are decorated and illustrated and at least one which has been described as a 'working copy'. I have studied these manuscripts closely, concentrating on finding similarities between them - particularly the appearance of the same hand in different manuscripts - which may point to a common place of production, possibly 'Gerald's scriptorium'. I have also considered the manuscript evidence for Gerald's publishing processes and the possibility of finding Gerald's autograph. I have then considered the manuscripts surviving from after Gerald's death and what they can show about the continuing tradition of his works, for example: who read them, and which were most popular; the geographical spread of the manuscript-evidence; whether different works were popular at different times, and why; the treatment of the works by later scholars, for example translation, abbreviation and excerpting. This includes evidence which I have discovered for the existence of now lost manuscripts. Finally, I have compared the manuscript-tradition of Gerald's works with that of some other twelfth-century Insular writers whose works survive in various authorial editions and/or in autograph or quasi-autograph copies.