This book constitutes the proceedings of the satellite events held at the 18th Extended Semantic Web Conference, ESWC 2021, in June 2021. The conference was held online, due to the COVID-19 pandemic.During ESWC 2021, the following six workshops took place:1) the Second International Workshop on Deep Learning meets Ontologies and Natural Language Processing (DeepOntoNLP 2021)2) the Second International Workshop on Semantic Digital Twins (SeDiT 2021)3) the Second International Workshop on Knowledge Graph Construction (KGC 2021)5) the 6th International Workshop on eXplainable SENTIment Mining and EmotioN deTection (X-SENTIMENT 2021)6) the 4th International Workshop on Geospatial Linked Data (GeoLD 2021).