What is Blockchain?
A shared digital ledger that records transactions across many computers so no single party can alter the history.
A blockchain is a ledger — a record of who sent what to whom — with one unusual property: instead of living inside one company's computer, identical copies live on thousands of computers at once, and they update in lockstep. Transactions are bundled into "blocks", each block is cryptographically chained to the previous one, and changing anything historical would mean re-doing the chain on most of the network's computers simultaneously. That's what people mean when they call it tamper-resistant.
The practical consequence is that strangers can transact without a bank in the middle vouching for the balance — the network itself is the referee. It's the invention underneath Bitcoin, Ethereum and every coin we track. It is not, despite a decade of marketing, a magic ingredient: a blockchain is only as useful as the thing it records, and plenty of projects bolted one onto problems that a normal database solved better.
Different blockchains make different trade-offs between speed, cost, decentralisation and programmability — which is most of what actually separates the major coins from each other.
See it in practice
Related terms: Bitcoin · Ethereum · Gas fees · full glossary
FAQ
Is blockchain the same thing as Bitcoin?
No — Bitcoin was the first use of a blockchain, but the ledger technology and the coin are separable. Thousands of blockchains now exist, each with its own coin, rules and trade-offs.
Can a blockchain be hacked?
Rewriting a major blockchain's history is practically infeasible — that part of the security has held. What gets hacked is everything around it: exchanges, bridges, wallets and people. The ledger is rarely the weak point; the endpoints are.
General information only, not financial advice. Definitions are maintained in our fact database and reviewed with the daily rebuild.