The aim of the present study is to paint an overall picture of how Voltaire interacted with the books that made up his personal library. Situated at the crossroads between history of the book, literary history and literary studies in the standard meaning of the term, it seeks to deepen our understanding of the ways in which Voltaire used his books and of the different types of notes that he left in them. These notes are of course texts in themselves – short ones, to be sure, but texts all the same – and their material, literary and polemical significance have never before been studied in depth. We begin by classifying the marginalia according to the function they seem to have played for Voltaire and, based on their material characteristics, by developing methodologies to analyse these short manuscripts, along with the non-verbal markings that accompany them. An analysis follows of the ways in which Voltaire used the white spaces in his books, then of the links that can be established between the signs of his reading and the genesis of his published works. Finally, we study the poetics of the marginal notes as well as the dynamics at work in the annotated library as a whole. Throughout, Voltaire’s notes and reading habits are placed in the context of the critical literature that has grown up around the subject of marginalia. Along the way, we compare his marginal notes to those of other literary figures of the period, for the subject of this study is clearly the marginalia of a writer, which are necessarily inextricably linked to his principal activity – writing. Indeed, one might speak of an interpenetration, of a blurring of boundaries between reading and writing. Beyond the marks of Voltaire's reading, the study of marginalia raises questions that are relevant for other non-canonical and paratextual materials. To place them in the spotlight transforms their status, and a note that was 'marginal' comes to be considered a text in its own right.