This note explains the key concepts relevant to blockchain and smart contracts, including distributed ledgers, cryptography, consensus and mining mechanisms, immutability, pseudonymity, disintermediation, the distinction between public and private blockchains, oracles and decentralised autonomous organisations. It considers the security issues and describes the key use cases associated with blockchain. It also covers the main legal issues associated with blockchain, including anti-money laundering, the legal status of cryptocurrency tokens, intellectual property, jurisdiction, data privacy, competition law, consumer protection, developer liability and smart contract enforceability. This note also briefly considers blockchain standardisation efforts.