This book constitutes the proceedings of the 23rd European Conference on Advances in Databases and Information Systems, ADBIS 2019, held in Bled, Slovenia, in September 2019. The 27 full papers presented were carefully reviewed and selected from 103 submissions. The papers cover a wide range of topics from different areas of research in database and information systems technologies and their advanced applications from theoretical foundations to optimizing index structures. They focus on data mining and machine learning, data warehouses and big data technologies, semantic data processing, and data modeling. They are organized in the following topical sections: data mining; machine learning; document and text databases; big data; novel applications; ontologies and knowledge management; process mining and stream processing; data quality; optimization; theoretical foundation and new requirements; and data warehouses.