Data sharing and interoperability are crucial for eliminating barriers to a digital single market within the EU, which is necessary to enhance the efficiency, transparency, and innovation of public services. Addressing these challenges helps prevent digital fragmentation and supports seamless data exchange, essential for digital transformation. To solve these challenges, the implementation of a coordinated approach across legislation, business processes, information management, and IT systems is required. Interoperability and common data standards must be prioritized to enable seamless communication between diverse systems and stakeholders, fostering effective data exchange and integration. This learning unit covers the fundamentals of data sharing and interoperability in the context of Local Digital Twins (LDTs). It explores the principles of legislation, technical frameworks, and organizational strategies necessary for implementing effective data sharing practices. The unit aims to empower learners with the knowledge to improve digital public services through better interoperability.