This book constitutes the refereed proceedings of the 38th International Conference on Conceptual Modeling, ER 2019, held in Salvador, Brazil, in November 2019.The 22 full and 22 short papers presented together with 4 keynotes were carefully reviewed and selected from 142 submissions. This events covers a wide range of topics, covered in the following sessions: conceptual modeling, big data technology I, process modeling and analysis, query approaches, big data technology II, domain specific models I, domain specific models II, decision making, complex systems modeling, model unification, big data technology III, and requirements modeling.