This article reports the findings of a 3 year research project which investigated disciplinary variation in student writing. Within an Open University course in the history of science, students from an arts background were found to achieve significantly higher grades than those from a science background. Textual and interview data suggest that differences in their essay writing may be related to differences in disciplinary culture and epistemology. The results thus support the hypothesis that students' writing is shaped by their disciplinary background, and call into question the extent to which communication skills are transferable across disciplinary contexts.