This book has one goal, to introduce theoretical and practical aspects of the blockchain technology. This book contains all material that is necessary to become a blockchain technical expert. Since the publication of the first edition of this book, a lot has changed and progressed further with regards to blockchain; therefore, a need to update the book has arisen. The multitude of benefits envisaged by the implementation of blockchain technology has sparked profound interest among researchers from academia and industry who are tirelessly researching this technology. As a result, many consortia, working groups, projects, and professional bodies have emerged, which are involved in the development and further advancement of this technology. The second edition of this book will provide indepth insights into decentralization, smart contracts, and various blockchain platforms such as Ethereum, Bitcoin, and Hyperledger Fabric. After reading this book, readers will be able to develop a deep understanding of inner workings of the blockchain technology and will be able to develop blockchain applications. This book covers all topics relevant to the blockchain technology, including cryptography, cryptocurrencies, Bitcoin, Ethereum, and various other platforms and tools used for blockchain development. It is recommended that readers have a basic understanding of computer science and basic programming experience to benefit fully from this book. However, if that is not the case then still this book can be read easily, as relevant background material is provided where necessary.