A blockchain is a distributed digital ledger that records data, commonly transactions, across a network of computers. Instead of relying on a single database controlled by one organization, a blockchain shares the same record among many participants, making it harder to alter history without detection.
How a blockchain works
A blockchain stores information in “blocks,” which are batches of data that get added over time. Each block typically contains a set of transactions, a timestamp, and a cryptographic fingerprint called a hash. Crucially, a block also includes the previous block’s hash, which links them together into a chain. If someone tries to change data in an older block, its hash changes, breaking the link to later blocks and revealing tampering.
To decide which new block is valid, networks use a consensus mechanism. In Proof of Work systems like Bitcoin, computers compete to solve a computational puzzle, and the winner proposes the next block. In Proof of Stake systems used by many newer networks, validators stake assets and are selected to propose and confirm blocks based on protocol rules. This consensus process helps independent nodes agree on one shared history.
What blockchains are used for
Blockchains are best known for powering cryptocurrencies, where the ledger tracks token balances and transfers without a central bank. For example, Bitcoin’s blockchain records who sent BTC to whom, while Ethereum and similar networks also support smart contracts, programmable code that can run decentralized applications such as lending protocols or NFT marketplaces.
Beyond finance, blockchains can be used to audit supply chains, verify credentials, or timestamp documents, especially when multiple parties need a shared record but do not fully trust one another. This concept matters because it enables digital ownership and coordination on the internet with transparency, verifiability, and reduced reliance on centralized intermediaries.