Blockchain is an emerging strategic frontier technology born with the rise of digital cryptocurrency represented by Bitcoin. At present, the blockchain field shows an obvious development trend that “theoretical research lags behind market practice”. To this end, this book is dedicated to a systematic and in-depth introduction to the basic theories and key methods of blockchain, covering blockchain data structures, P2P networks, cross-chain interoperability, consensus algorithms, economic incentives, smart contracts, capacity enhancement technologies, security and privacy protection, digital currencies and distributed ledgers.