This thesis is a study of the use of the ars dictaminis (the art of letter-writing) in fourteenth and early fifteenth century England. It has three aims: firstly to examine the extent to which the ars was an integral and important part of professional administration, ecclesiastical and secular; secondly to describe the nature of eloquent epistolary composition and compare this to the traditional requirements of the ars; and thirdly to investigate in the context of the preceding discussion the relationship between medieval rhetoric, middle English literature and renaissance humanism. The well documented career of Gilbert Stone, an episcopal chancellor, is used to initiate a wider investigation into those of his secretarial contemporaries. There is no evidence in later medieval England of a highly self conscious secretarial profession nor of a cult of eloquence. Letter collections point however to the importance of form and style, and an examination of their contents suggests that the rules of the ars. and particularly of the cursus, were used, adapted and developed, sometimes in quite routine documents, but more especially in 'eloquent' letters of persuasion. The ars, it is argued, was more vibrant, flexible and appropriate to its context than later critics have imagined. The ars, notably through Thomas Hoccleve, exercised an influence on poetic form and style; and even in a case such as that of Chaucer where there was not such a strong direct influence, it is possible that the ars may be seen as part of a complex conditioning literary environment. Finally the professional-literary structure underlying the use of the ars provided a motive and a means for the introduction of humanism into England.