Interoperability challenges impede the effectiveness of Local Digital Twins, as these complex systems falter when they cannot process diverse data sources. The challenge lies in ensuring that LDTs can reliably ingest and utilize data from disparate systems, enabling informed decision-making and collaborative governance across city services and infrastructure networks. To overcome the interoperability hurdle, the unit proposes using Minimal Interoperability Mechanisms (MIMs) and formal standards for data exchange. These solutions establish a common framework for technical, semantic, and organizational interoperability, allowing diverse systems to communicate, understand shared meanings, and coordinate effectively across institutional boundaries. The learning unit covers strategies to ensure interoperable LDT systems, starting with standards like CityGML and IFC. It explores semantic models, exchange protocols, and practical tools within the EU Local Digital Twin Toolbox, emphasizing the necessity of aligning sensor data with open standards and fostering cross-domain collaboration. This comprehensive approach enables robust digital twins capable of adapting to evolving city needs.