The two-volume set LNBIP 547 + LNBIP 548 constitutes the proceedings of the 19th International Conference on Research Challenges in Information Sciences, RCIS 2025, which took place in Seville, Spain, in May 2025. It focused on the special theme: Advancing Information Science and Information Systems Quality in the Era of Complexity. 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 33 full papers and 13 short papers included in the proceedings were carefully reviewed and selected from 103 submissions. They were organized in topical sections as follows:Part I: Information systems quality; security, risk and strategy; conceptual modeling and ontologies; modeling methods and requiremments engineering; databases informaiton management; human factors in information systems; business process engineering and management; Part II: Machine-learning and generative AI applications; RCIS Forum; and RCIS Doctoral Consortium.