What Is a Blockchain, and How Does It Work in Bitcoin? A blockchain is a type of distributed database that stores information in a sequence of blocks. In the context of Bitcoin, the blockchain is a public record of confirmed transactions that is maintained and independently verified by network participants. Each block contains a group of valid Bitcoin transactions, along with other data required to connect that block to the existing chain. The term blockchain comes from this structure: information is stored in individual blocks, and each new block is cryptographically linked to the previous one. How are blocks connected? Every Bitcoin block contains a reference to the previous block through its block header. This reference is based on a cryptographic hash. A hash is a fixed-length output generated from data. If the underlying data changes, the resulting hash also changes. Because each block refers to the previous block, changing historical data would break the links...