Consensus

Consensus is the set of rules a blockchain uses to get thousands of independent, mutually distrusting computers to agree on a single shared transaction history without a central referee. Instead of a bank or company confirming who owns what, the network itself decides collectively, and once enough participants accept a block, it becomes practically permanent and cannot be quietly rewritten.

Different blockchains reach that agreement differently. Bitcoin was the first to solve the problem at real scale, requiring miners to spend computing power solving a hard puzzle before they can add a block, a design that traces back to the theoretical Byzantine Generals Problem of coordinating trust between parties who might lie. Many newer networks, including Ethereum since its 2022 Merge, instead have validators lock up coins as collateral, with dishonest or lazy behaviour punished by losing part of that stake. Both approaches make cheating expensive: an attacker generally needs to control a majority of either computing power or staked capital to impose a false version of the ledger, which is why the threshold is often loosely described as "51%."

Consensus matters because it replaces a trusted middleman with math and economic incentives, letting a network stop double-spending and settle disputes automatically. Variants such as delegated proof of stake and practical Byzantine fault tolerance trade decentralization, speed and energy use against each other in different ways. When operators cannot agree on the rules at all, the chain can split into a hard fork, producing two separate histories. Smaller, newer chains remain far more exposed to majority-control attacks than large, established networks.