Research that has examined university assignment writing has varied from large-scale, inventorial surveys across disciplines to more specific, finer-grained analyses of the assignment requirements of specific disciplines. However, while such research has involved surveys of the views and expectations of faculty or the analysis of assignment tasks, less attention has been given to the written texts that are the outcomes of assignment tasks. Furthermore, previous studies have not tended to employ theories of text or discourse in systematic ways to account for the organisational and linguistic resources employed in assignment writing. In addressing these issues, this study examines the essay as an assignment genre in the disciplines of sociology and English. For each discipline, a sample of ten extended student essays, taken from the "British Academic Written English (BAWE) Corpus," is examined in terms of the dual approach to genre (social and cognitive) of Bruce (2008a). Each essay text is subject to close analysis of the rhetorical purposes, discoursal and textual resources that it draws upon. The findings of the study indicate significant differences between the essay genre in the two disciplines in the complex variety of rhetorical purposes and associated textual resources that they draw upon.