This is a study of the letters of Anne, countess of Northumberland (1536–91) throughout her exile in the Low Countries from August 1570 until her death on 9 September 1591. The thesis draws on archival research and analysis of several hundred letters and associated documents, in English, Latin, Scots, French and cipher, spread across six British and European archives, to, from and about Anne and her contemporaries. The thesis includes an edition of the twenty-four extant letters written to and from Anne, in English and Latin, and images of these, as well as a newly published ODNB entry. Anne's letters offer evidence of an early modern woman directing and commanding the production and rhetorical construction of her correspondence and the gendered nature of her epistolary world. The thesis argues that she successfully represented herself and developed her agency despite (or in the context of) epistolary practices shaped heavily by men: male secretaries penned her letters, male addressees and male intelligencers intercepted and assessed the value of her correspondence. This thesis illuminates the physical ways that Anne authorised her letters as well as the rhetorical and linguistic strategies that she employed to assert her own power and negotiate her position in epistolary exchanges. After the introduction, which includes a biography of Anne, an overview of her letters and an outline of the theoretical framework of the thesis, there are three analytical chapters. Chapter One situates the letters in their socio-historical contexts to highlight how Anne negotiated the extreme circumstances of her exile to her own advantage: to access traditional reward-based patronage; to deploy informal shared experiences to sustain service and client bonds; and to establish a central position within the English exile community and the political network surrounding Mary, Queen of Scots. Chapter Two draws on techniques from manuscript studies and examines Anne's letters and the evidence they offer for their own composition, sending, reception and afterlife. This chapter reveals the benefits of close scrutiny of the physical and linguistic features of letters, adding detail to our understanding of women's use of letter-writing practices in the period. Chapter Three applies techniques from the field of historical pragmatics to analyse the rhetorical and linguistic strategies used in Anne's letters to bolster her own position by appropriating gender expectations to her own advantage while navigating social and interpersonal relationships embedded in epistolary exchanges. The thesis therefore, by drawing on different disciplinary techniques, offers us layers of insights into the letters. The picture that emerges is one that depicts not only Anne's agency but the processes through which her agency was constructed and enacted, according to the opportunities and limitations of her own culture and the extreme and exceptional circumstances of her own life.