An important component of fluent linguistic production is control of the multi-word expressions referred to as clusters, chunks or bundles. These are extended collocations which appear more frequently than expected by chance, helping to shape meanings in specific contexts and contributing to our sense of coherence in a text. Bundles have begun to attract considerable attention in corpus studies in EAP, although the extent to which they differ by discipline remains an open question. This paper explores the forms, structures and functions of 4-word bundles in a 3.5 million word corpus of research articles, doctoral dissertations and Master's theses in four disciplines to learn something of disciplinary variations in their frequencies and preferred uses. The analysis shows that bundles are not only central to the creation of academic discourse, but that they offer an important means of differentiating written texts by discipline.