Wikidata ( Communications of the ACM 57 (2014) 78–85), the open knowledge graph maintained by the Wikimedia Foundation, continues to expand its role as a central hub of structured data for Wikipedia and its sister projects, as well as an increasingly vital resource for academic research and industrial applications. Its collaborative nature, blending human and machine contributions, creates unique opportunities and challenges at the intersection of knowledge representation, data management, and socio-technical systems. The growing academic interest in Wikidata has been exemplified by initiatives like the annual Wikidata Workshop at the International Semantic Web Conference (ISWC) (Proceedings of the 4th Wikidata Workshop (2024) CEUR Workshop Proceedings; Proceedings of the 3rd Wikidata Workshop (2023) CEUR Workshop Proceedings). These efforts have fostered a vibrant research community investigating both the technical aspects of Wikidata and its socio-technical ecosystem. Building on this momentum, this special issue of the Semantic Web Journal brings together cutting-edge research to explore the opportunities and challenges posed by this collaborative knowledge graph.