Consensus mechanisms are protocols used in blockchain networks to achieve agreement among participants on the state of the ledger. They ensure that all transactions are verified and recorded accurately, preventing issues like double-spending. Common types include Proof of Work and Proof of Stake, each with its own method for validating transactions and securing the network. These mechanisms play a crucial role in maintaining the integrity and security of decentralized systems. By requiring participants to follow specific rules, consensus mechanisms help build trust among users, enabling them to collaborate without needing a central authority.