A consensus mechanism is a process used in blockchain networks to achieve agreement among participants on the state of the network. It ensures that all transactions are verified and recorded accurately, preventing issues like double-spending. Common types of consensus mechanisms include Proof of Work and Proof of Stake, each with its own method for validating transactions and securing the network. These mechanisms are crucial for maintaining the integrity and security of decentralized systems. By requiring participants, or nodes, to follow specific rules, consensus mechanisms help build trust among users without the need for a central authority. This decentralized approach is fundamental to the operation of cryptocurrencies like Bitcoin and Ethereum.