This two-volume set LNCS 16549 + 16550 constitutes the refereed proceedings of the 23rd European Semantic Web Conference, ESWC 2026, held in Dubrovnik, Croatia, during May 2026. The papers presented were carefully reviewed and selected for inclusion in the book. For the research track 28 papers have been accepted from 116 submissions; the resources track received 63 submissions of which 17 have been accepted; and for the In-use track 10 papers are included from 27 submitted. The ESWC’s Research track addresses the theoretical, analytical, and empirical aspects of the semantic web, semantic technologies, knowledge graphs and semantics on the Web in general. The In-use track focuses on contributions that reuse and apply state-of-the-art semantic technologies or resources to real-world settings. The resource track deals with resource contributions that are, on the one hand innovative or novel, and on the other hand sharable and reusable (e.g. datasets, knowledge graphs, ontologies, workflows, benchmarks, frameworks), and provide the necessary scaffolding to support the generation of scientific work and advance the state of the art.