Consensus mechanism

A consensus mechanism is the set of rules through which participants in a distributed system agree on a state and an order of operations. It defines how changes are proposed and validated and how disagreements are resolved. Its guarantees depend on the fault model and security assumptions.

Written by Pablo Gómez

Founder & CEO at Metlabs · Reviewed on October 11, 2026

A blockchain consensus mechanism usually combines two layers. The first is Sybil resistance, defining who can propose a block: PoW ties it to computation, PoS to capital, other models to authority or identity. The second is fork choice and finality, defining which chain is canonical and when it becomes irreversible: Bitcoin's longest-chain rule, or the combination of LMD-GHOST and Casper FFG in Ethereum.

A key family is Byzantine Fault Tolerance (BFT), which tolerates up to f malicious nodes out of 3f+1 total, meaning it requires the agreement of more than two thirds. PBFT, described by Castro and Liskov in 1999, is the classic reference; Tendermint/CometBFT is its modern blockchain realization, with instant per-block finality. Consensus is the property that turns a replicated database into a blockchain: without it there is no single state nor immutability, and it defines the security model, the degree of decentralization and the confirmation latency of the entire network.

For tokenization of real-world assets this is decisive: the irreversibility guarantees on which on-chain ownership rests never exceed those of the underlying consensus. Bitcoin uses Nakamoto consensus with PoW; Ethereum uses Gasper with PoS; Cosmos and Celestia use CometBFT with instant finality; and permissioned networks such as Hyperledger Fabric use modular consensus, relevant in enterprise cases. Ethereum's Merge, on 15 September 2022, was precisely a change of consensus mechanism, from PoW to PoS.