This article considers the notion of "academic vocabulary": the assumption that students of English for academic purposes (EAP) should study a core of high frequency words because they are common in an English academic register. We examine the value of the term by using Cox-head's (2000) Academic Word List (AWL) to explore the distribution of its 570 word families in a corpus of 3.3 million words from a range of academic disciplines and genres. The findings suggest that although the AWL covers 10.6% of the corpus, individual lexical items on the list often occur and behave in different ways across disciplines in terms of range, frequency, collocation, and meaning. This result suggests that the AWL might not be as general as it was intended to be and, more importantly, questions the widely held assumption that students need a single core vocabulary for academic study. We argue that the different practices and discourses of disciplinary communities undermine the usefulness of such lists and recommend that teachers help students develop a more restricted, discipline-based lexical repertoire. (Contains 7 tables and 1 footnote.)