What will happen if blockchains can’t exchange data with each other? In order to answer the question, this chapter delves into the crucial topic of blockchain interoperability and how it plays a critical role in the evolution of Web 3.0. Bitcoin, Ethereum and Hyperledger are the three most well-known blockchain networks. This chapter commences with a study of their interoperability. The need for smooth interoperability is made apparent by the many real-world applications in various industries, including non-financial (supply chain, healthcare, IoT) and financial (DeFi, CBDCs). This chapter looks at a number of solutions, including message-passing protocols, atomic exchanges, relays, and bridges. This chapter also discusses scalability in connection to interoperability. Web 3.0, a user-driven, decentralized, and interoperable ecosystem that permits the safe exchange of identities, assets, and applications among its chains, is discussed at the chapter’s conclusion.