This book constitutes the refereed post proceedings of the 18th Research Conference on Metadata and Semantic Research, MTSR 2024, held in Athens, Greece, during November 19-22, 2024. The 23 full papers and 6 short papers included in this book were carefully reviewed and selected from 59 submissions. These papers were organized in the following sections: track on metadata, linked data, semantics and ontologies - general session; track on open repositories, research information systems & data infrastructures; track on digital libraries, information retrieval, big, linked, social & open data; track on cultural collections & application; track on european and national projects; and 8th dOAbLE - papers for libraries, archives,museums; track on agriculture, food & environment (agroSEM'24); track on digital humanities and digital curation.