My study investigates aspects of the idiolect of Queen Elizabeth I using a sociolinguistic framework. My source material for Elizabeth's idiolect is an electronic corpus which I have compiled from transcripts of the best-authenticated examples of Elizabeth's own compositions in letters, speeches and translations. My investigation analyses nine morpho syntactic variables in the corpus and I chart their distribution and development diachronically. I also provide the first detailed analysis of Elizabeth's spelling, assessing developments in forms and the level of consistency in their use. For each linguistic feature, I compare her idiolect with macro-level linguistic data in order to contextualise her usage within previously established statistical norms of Early Modern English. I conduct a detailed analysis of social, stylistic, interactive and systemic factors to assess their potential influence on the frequency patterns in her idiolect. There are three key outcomes of my study. Firstly, I offer a new perspective on Elizabeth's writing by considering how the linguistic developments in her idiolect reflect and relate to her biographical experiences. I re-evaluate the emphasis historians have placed on her accession, and identify other biographical events that appear to have an impact on her language-use. I also consider how far Elizabeth's role in language change (where she is often a leader and frequently comparable in usage to her male contemporaries) affects current accounts of her socio-political role as a female monarch. Secondly, I evaluate the applicability of my idiolectal data to questions of authorship in the canon of Elizabeth's writings, considering the theoretical merits of morpho syntactic and spelling data before testing its application with four case studies. Thirdly, I reflect on the role of the idiolect in historical sociolinguistics, and demonstrate how my findings can test existing sociolinguistic accounts, and help to expand our understanding of the processes involved in language change.