What Is a Blockchain?

A blockchain is a shared record of transactions that no single party can quietly edit. Think of it as a public spreadsheet that thousands of computers each keep a copy of and constantly check against one another.

Transactions are bundled into blocks. Each new block includes a cryptographic fingerprint of the block before it, linking them into a chain. Changing an old transaction would change every fingerprint after it — so tampering is immediately obvious to the rest of the network.

Because everyone holds the same copy and agrees on the rules, the blockchain becomes a single source of truth without a central authority. This is what lets strangers transact directly, and what makes balances and history auditable by anyone. Different blockchains make different trade-offs between speed, cost, and decentralization, which is why Bitcoin, Ethereum, and newer networks behave so differently.