As the editors of this volume have attested, library catalogues have existed in electronic form since at least the 1960s. The transition from analogue to electronic catalogue significantly strengthened the ability of libraries the world over to administer collection development and access at the local, regional, national and even international level. While the electronic catalogue has long helped libraries realise a range of administrative functions, it has been less common for the library catalogue to be treated as data for research inherently suited to disciplinary inquiry that leverages computational methods at macro and microscopic scales. A library catalogue is not an archive, but it bears a similarity in the sense that it records the organic activities of an organisation that just happens to shape epistemic and ontological awareness through its regular operations. A library catalogue is an accretion, a fossil record of subjective decisions that evidence what an organisation operating in a particular sociocultural context believes is important and, consequently, what is not important. The library catalogue channels contested collection descriptions that directly influence how communities encounter and assess knowledge, circulation data complicates any sense of certainty with respect to the zeitgeist, and in the aggregate, library catalogues provide a dynamic map that characterises the waxing and waning of knowledge production globally. Library Catalogues as Data: Research, Practice and Usage introduces a diverse range of contributions that speak directly to these affordances and more.