This thesis argues that marginalia, understood broadly as those writings to be found on the margins of the literary work or text, can help us to rethink a number of practical and theoretical issues that have been, and remain, central to the discipline of English Studies: from the formalist strictures on intrinsic/extrinsic evidence, to poststructuralist notions of textuality, to the more recent turn to 'affect', and the re-emergence of archival forms of research as a possible alternative to 'Theory' altogether. By bringing together three forms of literary annotation - reading notes, manuscript marginalia, and fictional footnotes - my thesis argues for the usefulness of a dynamic model of 'centre' and 'margin' for theorizing interpretation as a problem of ideological investment: in other words, I take any margin ('material' or otherwise) to be constituted in opposition to a 'centre' that is a matter of socio-historical perspective, rather than simply 'given'. I begin by contending that the value and meaning of authorly annotations have tended to proceed from Romantic notions of authority: the marginal note assumes a synecdochic relation to the author as a 'whole'. However, I argue that this framework has historically tended to allow the marginal note to act as a kind of 'transparent' supplement to interpretation, while at the same time masking a number of potentially problematic assumptions. For example, whereas the annotations of William Blake and James Joyce have usually stood as evidence of aesthetic mastery, those of Sylvia Plath and Djuna Barnes have only tended to buttress their authors' cultural positioning as stereotypically 'dangerous' or 'embittered' female artists. In this sense, while the thesis does not posit any straightforward equivalence between textual and 'other' kinds of marginality (e.g. political), nor does it dismiss their connection entirely; indeed, it goes on to argue that such divergent forms of 'marginality' have often been brought into conjunction by the appearance of pseudo-scholarly marginalia in the literary text, from Alexander Pope to T. S. Eliot to Susan Daitch. The main 'case study' of the thesis builds on these claims to contend that the work of David Foster Wallace, as well as its reception, occupies a central position in a wider cultural reaction to the 'radical de-centrings' of Marxist and psychoanalytical post-structuralism. Chapter One argues that Wallace's extensively annotated personal library - several items from which were controversially redacted by the Ransom Centre in 2011 - can be seen to participate in a critical return to the category of the (white, male, middle-class) 'genius' that is nonetheless critiqued in advance by his work; engaging with Fredric Jameson, I thus contend that Wallace's marginalia perform both the 'end of the bourgeois ego' and its rejuvenation. Chapter Two argues that this tension is exacerbated by a reading of Wallace's 'unfinished' posthumous novel, The Pale King, alongside its archival materials. Rather than allowing us to 'disentangle' the author's intentions from his editor's interference, the movement between oeuvre and archive instead draws the 'original/mediated' opposition into the problems of aesthetic 'plagiarism' and late capitalist abstraction that run throughout Wallace's writing. And finally, although Wallace's oeuvre seems persistently to attempt to supersede such tensions through its extensive use of pseudo-scholarly footnotes, yet Chapter Three argues that these same marginalia tend to reinscribe a set of anxieties around autonomous selfhood, 'affect', and cultural value that is inseparable from the modern institutionalization of U.S. literary production and 'critical theory'.