We are happy to bring you this special issue of Data and Knowledge Engineering based on the 34th International Conference on Conceptual Modeling (ER 2015), which was held on 19–22 October 2015 in Stockholm, Sweden. Since 1979, when its first edition was held in Los Angeles, the ER conference has been the flagship conference series and the premier international meeting space for the Conceptual Modeling community. In 2015, the conference attracted 131 submissions from all parts of the world, 41 of which were accepted as long and short papers. The technical program also included four keynotes, nine workshops, five tutorials, a Ph.D. colloquium, a demo session, and a panel session. The conference covered a broad range of areas in conceptual modeling, from ontology-based modeling and data model semantics to conceptual modeling for big data and applications of modeling in health and social care.