This book constitutes extended, revised and selected papers from the 21st International Conference on Enterprise Information Systems, ICEIS 2019, held in Heraklion, Crete, Greece, in May 2019. The 26 papers presented in this volume were carefully reviewed and selected for inclusion in this book from a total of 205 submissions. They deal with topics such as data science and databases; ontologies; social networks; knowledge management; software development; human-computer interaction, and multimedia.