Ontologies and Reasoning -- Streaming Partitioning of RDF Graphs for Datalog Reasoning -- Parallelised ABox Reasoning and Query Answering with Expressive Description Logics -- Analysing Large Inconsistent Knowledge Graphs using Anti-Patterns -- Processing SPARQL Property Path Queries Online with Web Preemption -- Ontology-Based Map Data Quality Assurance -- Knowledge Graphs (Understanding, Creating, and Exploiting) -- Applying Grammar-based Compression to RDF -- HDT Bitmap Triple Indices for Efficient RDF Data Exploration -- Programming and Debugging with Semantically Lifted States -- Do Embeddings Actually Capture Knowledge Graph Semantics? -- A Semantic Framework to Support AI System Accountability and Audit -- Semantic Data Management, Querying and Distributed Data -- Comparison Table Generation from Knowledge Bases -- Incremental Schema Discovery for RDF Data at Scale -- HTTP Extensions for the Management of Highly Dynamic Data Resources -- Expressibility of OWL Axioms with Patterns -- Data Dynamics, Quality, and Trust -- Refining Transitive and pseudo-Transitive Relations at Web Scale -- Data Reliability and Trustworthiness through Digital Transmission Contracts -- Matching, Integration, and Fusion -- Neural Knowledge Base Repairs -- Natural Language Inference over Tables: Enabling Explainable Data Exploration on Data Lakes -- NLP and Information Retrieval -- Grounding Dialogue Systems via Knowledge Graph Aware Decoding with Pre-trained Transformers -- WEB-SOBA: Word Embeddings-Based Semi-automatic Ontology Building for Aspect-Based Sentiment Classification -- Context Transformer with Stacked Pointer Networks for Conversational Question Answering over Knowledge Graphs -- Machine Learning -- Neural Multi-Hop Reasoning With Logical Rules on Biomedical Knowledge Graphs -- Augmenting Ontology Alignment by Semantic Embedding and Distant Supervision -- Convolutional Complex Knowledge Graph Embeddings -- RETRA: Recurrent Transformers for Learning Temporally Contextualized Knowledge Graph Embeddings -- Injecting Background Knowledge into Embedding Models for Predictive Tasks on Knowledge Graphs -- Science Data and Scholarly Communication -- Structured Semantic Modeling of Scientific Citation Intents -- Discovering Research Hypotheses in Social Science using Knowledge Graph Embeddings -- Problems to Solve Before You Die -- Towards a Linked Open Code -- A Polyvocal and Contextualised Semantic Web -- Resources -- The WASABI dataset: cultural -- RuBQ 2.0: An Innovated Russian Question Answering Dataset -- A Knowledge Organization System for the United Nations Sustainable Development Goals -- RSP4J: An API for RDF Stream Processing -- WasmTree: Web Assembly for the Semantic Web -- ParaQA: A Question Answering Dataset with Paraphrase Responses for Single-Turn Conversation -- kgbench: A Collection of Knowledge Graph Datasets for Evaluating Relational and Multimodal Machine Learning -- The SLOGERT Framework for Automated Log KnowledgeGraph Construction -- P2P-O: A Purchase-To-Pay Ontology for Enabling Semantic Invoices -- KOBE: Cloud-native Open Benchmarking Engine for Federated Query Processors -- CSKG: The CommonSense Knowledge Graph -- In-Use Track -- A Knowledge Graph-based Approach for Situation Comprehension in Driving Scenarios -- Pay-as-you-go Population of an Automotive Signal Knowledge Graph.

This book constitutes the refereed proceedings of the 18th International Semantic Web Conference, ESWC 2021, held virtually in June 2021. The 41 full papers and 2 short papers presented were carefully reviewed and selected from 167 submissions. The papers were submitted to three tracks: the research track, the resource track and the in-use track. These tracks showcase research and development activities, services and applications, and innovative research outcomes making their way into industry. The research track caters to both long-standing and emerging research topics in the form of the following subtracks: ontologies and reasoning; knowledge graphs (understanding, creating, and exploiting); semantic data management, querying and distributed data; data dynamics, quality, and trust; matching, integration, and fusion; NLP and information retrieval; machine learning; science data and scholarly communication; and problems to solve before you die.