A consensus mechanism is the set of rules and protocols a blockchain network uses to achieve agreement among distributed nodes on the valid state of the ledger – determining which transactions are valid and in what order they occurred. Consensus mechanisms solve the Byzantine Generals Problem: how can a network of participants who may include malicious actors still reach reliable agreement? The choice of consensus mechanism fundamentally shapes a blockchain security, speed, decentralisation, and energy use. Major types include: Proof of Work (Bitcoin) – computational cost creates security; Proof of Stake (Ethereum, Cardano) – economic stake creates security; Delegated Proof of Stake (TRON, EOS) – voted delegates validate for efficiency; Proof of Authority (enterprise chains) – trusted validators provide efficiency with less decentralisation; Proof of History (Solana) – cryptographic clock enables speed; Tendermint BFT (Cosmos) – instant finality with two-thirds supermajority. The blockchain trilemma (coined by Vitalik Buterin) states that a blockchain can optimise for at most two of three properties simultaneously: security, scalability, and decentralisation. Consensus mechanisms represent different trade-offs along this trilemma.
Example: Example: Bitcoin chose Proof of Work: maximising decentralisation and security at the expense of speed (7 TPS) and energy efficiency. Solana chose Proof of History plus PoS: maximising speed (65,000 TPS) at some cost to decentralisation (fewer validators). Neither is objectively better – each reflects different prioritisation of the blockchain trilemma.
Learn more: Ethereum.org – Consensus Mechanisms
