Library catalogues have existed for centuries, and in electronic form since at least the 1960s. They facilitate bibliographic management, description, discovery and access. The advent of web-scale discovery, however, has led to a redefinition and complication of the role of the library catalogue as it becomes just one part of a complex portfolio of full-text subscription resources, metadata and finding aids, multimedia content, digitised archival materials, web resources and publisher information. This web of library collections, federated content, and myriad self-contained digital resources represents a fragmented ecosystem of interrelated technologies, metadata standards, federated content and resource typologies that represents institutional as well as commercial interests. At the same time, each of these strands of the web produces data relating to a range of library activities, including but not limited to bibliographic description and classification, collection development, purchasing, user accounts and interactions with the library and its resources. As a result, libraries are repositories not only for physical and digital information resources, but for enormous amounts of data about the interactions between those resources and human actors, such as library staff and users. Researchers are, as a result, already using library data sources, including historical and contemporary catalogues, borrowing records, library classification data and metadata, in their research.