This book constitutes the refereed post proceedings of the 19th Research Conference on Metadata and Semantic Research, MTSR 2025, held in Thessaloniki, Greece, during December 15–19, 2025.

The 30 full papers and 3 short papers included in this book were carefully reviewed and selected from 84 submissions. They organized in the following topical sections as follows Artificial Intelligence, Large Language Models, and Semantic Technologies for Applied Metadata, Decision Support, and Digital Repositories; Knowledge Organization, Metadata Standards, Linked Data, and Knowledge Graphs; Semantic Interoperability and Research Infrastructures: CIDOC CRM, Provenance, Ontological Modelling, and Open Repositories; Digital Libraries, Knowledge Extraction, and Open Data; Metadata and Semantic Technologies for Agriculture, Food, and Environmental Applications; Digital Humanities, Cultural Semantics, and Intelligent Surveillance Systems and Metadata, Ontologies, and AI for GLAM Institutions: Innovation in Libraries, Archives, Museums, Art and Music Collections, and Cultural Heritage Data Spaces.