This book constitutes the proceedings of the 20th International Conference on Research Challenges in Information Science, RCIS 2026, which took place in Toulouse, France, during May 2026. The scope of RCIS is summarized by the thematic areas of information systems and their engineering; user-oriented approaches; data and information management; business process management; domain-specific information systems engineering; data science; information infrastructures, and reflective research and practice.The 37 full papers included in this volume were carefully reviewed and selected from 116 submissions. The papers have been divided into the following topical sections: Human Trust, Privacy, and Ethical AI Usage; Process Mining, Modeling, and Intelligent BPM Systems; Machine Learning and AI Systems Engineering; Advanced Data Processing; Intelligent Systems Applications; Intelligent Systems: From Search to Decision Support; Requirements Engineering for Secure and Safe Systems; and Modeling and Representation of Digital Systems.