L2 student writers in UK universities often seek the services of a 'proofreader' before submitting work for assessment, and the proliferation of freelance proofreaders and online proofreading agencies has led to debates about the ethics of the proofreading of student writing in publications such as Times Higher Education. This study investigates the kinds of ethical issues that confront proofreaders and how they deal with them. Nine UK university proofreaders proofread the same poor-quality L2 applied linguistics master's essay, explaining their interventions by talking aloud while proofreading and at a subsequent interview. Proofreaders addressed ethical difficulties by means of two macrostrategies: (i) selective proofreading; and (ii) declining to proofread in part or in whole. Two additional findings relating to ethics emerged from the study: firstly, some informants experienced dilemmas and uncertainties despite their attempts to proofread ethically; secondly, a number of informants went far beyond traditional, narrow conceptualizations of proofreading, making interventions affecting the writer's structure, argumentation, and content which could be seen as unethical. The findings highlight the need for the regulation of proofreading to ensure it is standardized and consistently administered from writer to writer, and I close by recommending that universities strive to implement more formative types of proofreading to enhance writers' academic literacy, not just their texts.found that in their UK university context, proofreading was unregulated: anyone could set themselves up as a proofreader regardless of qualification, experience, knowledge, or training. Nor were proofreaders obliged to agree to abide by a set of regulations as to how they would intervene in a text, raising concerns about the potential for substantial and unethical interventions. This situation is not unique: Baumeister (2014) laments the 'unregulated state of the editing industry in South Africa' and claims the lack of said regulations and guidance for proofreaders of student writing 'counteract[s]…professional and accurate editing' (p.2). Happily, things appear to have changed in the UK since Harwood et al.'s study, in that an increasing number of universities have formulated proofreading policies which are publicly available on their websites: see, for instance, the policies of the London School of Economics, 1 the University of Warwick, 2 and the University of Oxford. 3 Yet despite the increasing regulation, ethical issues remain: Harwood et al. (2009) claimed that much proofreading is done by institutional outsiders, i.e., writers' family, friends, or freelance proofreaders with no connection to the university in question, and these outsiders may have little knowledge of proofreading policies and the degree to which the institution permits them to intervene. In addition, there is increasing evidence that proofreaders have differing understandings of their role and of the extent to which they should intervene (Harwood 2018;Harwood et al....