What Is Blockchain?
A blockchain is a shared digital ledger — a running list of transactions — that isn’t stored in one place. Instead, many independent computers (called nodes) each keep a full copy, and they all follow the same rules to agree on what the ledger says. That’s the entire innovation: agreement without a central referee.
Blocks and hashes
Transactions are grouped into "blocks." Each block contains a cryptographic fingerprint (a "hash") of the block before it, chaining them together in order — hence "blockchain." Changing anything in an old block would change its hash, which would break every block after it, making tampering immediately obvious to anyone checking.
Why no single point of control
Because thousands of nodes each hold an identical copy of the ledger, there’s no single server to hack, shut down, or quietly edit. To alter the accepted history, an attacker would need to overpower the majority of the network’s computing power or stake simultaneously — which is designed to be prohibitively expensive on any well-established network.
Consensus: Proof of Work vs. Proof of Stake
Networks need a way to agree on which new block is valid. Proof of Work (used by Bitcoin) has computers compete to solve a computational puzzle, consuming real electricity as a cost of participation. Proof of Stake (used by Ethereum since 2022) instead has participants lock up (“stake”) cryptocurrency as collateral, with dishonest behaviour penalised by losing that stake — achieving similar security with far less energy use.
Beyond currency
While blockchain was invented for Bitcoin, the same idea — a shared, tamper-evident ledger anyone can verify — now underpins DeFi lending protocols, NFTs, and increasingly experiments in supply-chain tracking and digital identity, well outside cryptocurrency alone.
Not investment advice
This page is general information for education only, not investment, legal, or tax advice. Rules and risks can change — do your own research and consult a qualified professional before acting on anything here.