This thesis examines the use of vocabulary in the Book of Margery Kempe, as a means of exploring register in the context of autohagiography. It analyses the way in which Margery ascribes words to different protagonists in her work, the register from which these words are drawn, and the resonances that they have when applied to the protagonists. The aim is to understand how Margery seeks to represent herself as a medieval holy woman, and how she positions herself in relation to the Book's principal protagonists; both the personae who inhabit her visionary world, and the men and women she encounters in reality. The thesis assumes that the Book can be read as a work of autohagiography, and therefore raises a second question: does Margery manipulate register in such a way as to enhance her own holiness so that she comes to be seen as the saintly protagonist of her own vita? The thesis, therefore, whilst having a linguistic concern, should primarily be understood as a work of literary criticism. The original research of this thesis is contained within its appendix, in which the words of the Book have been etymologically derived and dated according to first recorded usage entries in both the Oxford English Dictionary and the Middle English Dictionary. The dates, whilst not infallible (there are points of disparity between the two dictionaries, and points where entries cited post-date 1438) provide a useful guide as to the age of a word, and from this one can surmise its register. On this basis, the thesis then tackles assumptions that naturally arise: if we take the major personae of the Book, a supposition would be that Margery, the 'humble creatur', would use a vocabulary that reflected her humility, drawn from Old English and naturalised French. A second assumption might be that Christ, an exalted figure, would be given a vocabulary that reflected his status: Latinate and sophisticated, to exemplify his elevated position and to provide necessary contrast between himself and Margery. The difference in their statuses would, therefore, be demonstrated via their vocabulary. The Virgin Mary, moreover, plays a significant role within the work, and one might assume that her vocabulary would mirror that of her son: divinely elevated, with Margery occupying a position beneath her. Closer investigation, however, suggests that these assumptions are open to question. As this thesis will highlight, Christ's vocabulary is that of an everyman, both sophisticated and humble, and he is even capable of employing specific and highly localised words pertaining to fourteenth-century Lynn. Margery's vocabulary comprises some extremely stylish Latinate and later French importations, suggesting that her humility is not as absolute as she presents. Mary, moreover, is given a lexical range that is almost entirely made up of Old English and early French imports. This could be consistent with her position as the humblest of all biblical characters in her suffering, sorrow and forbearance; or it could be seen as a subtle undermining of her status by Margery who consciously shifts her own vocabulary upwards in order to usurp Mary's position. This thesis, therefore, seeks to explore the various literary issues that result from a close linguistic survey, and to explore these issues within a framework that discusses whether the use of register ultimately supports the view that Margery's work was intended to be read as autohagiography. The thesis begins with two contextualising chapters on medieval Lynn, its religious houses, and the evolution of medieval traditions of female piety and mysticism, so that Margery may be purposefully situated within her social, religious, and broader cultural milieux (which naturally informs her use of vocabulary), before turning its attention to chapters that scrutinise the use of vocabulary in various contexts. These include the vocabulary of Christ in relation to Margery; the words of the other women whom Margery encounters, particularly the Virgin Mary; the language of virginity and the virgin saints; and the language of Margery's persecutors. The conclusions that can be drawn from each suggest that there was register awareness on Margery's part, and that this register awareness is reflected in the Book's characterisations of its principal protagonists. This, in turn, can suggests strongly that the Book was intended to represent Margery's claim sainthood.