In many European countries, librarians and researchers are working to compile a detailed bibliographic overview of early modern books printed within a defined time frame and within territorial and linguistical boundaries: they are creating modern retrospective 'national' bibliographies. The contributions from 14 countries in this publication illustrate this rich and diverse activity and demonstrate the various approaches in the digital age. Their approaches are anchored in the past, as each 'national' bibliography defines its scope within a careful analysis of the history of the country or nation, and rely on present-day cataloging, study of book history and new possibilities in the digital environment. The Consortium of European Research Libraries (CERL) strongly supports data aggregation (as reflected in the data network it maintains) and data linking. Improved interoperability today supports opening of data and making it available beyond silos and databases. This is therefore a good time to provide an overview of the European data landscape for retrospective 'national' bibliographies, as these contain valuable and sustainable data with an impact on the semantic universe. They are closely related to research, are quality-controlled, provide reliable data and are rich in content. Their interaction with other library data, e.g. through authority control or thesauri, but also through copy-specific information, has the potential to considerably expand the role of retrospective bibliographies in the research areas. This will be a challenge for their ongoing development and sustainability and explains the title of this book Never Finish(ed) !