Consensus algorithms are protocols used in computer networks to achieve agreement among distributed systems. They ensure that all participants in a network, such as nodes in a blockchain, agree on a single data value or state, even in the presence of failures or malicious actors. This is crucial for maintaining the integrity and reliability of decentralized systems. There are various types of consensus algorithms, including Proof of Work, Proof of Stake, and Practical Byzantine Fault Tolerance. Each has its own method for validating transactions and securing the network, balancing factors like speed, security, and energy efficiency to meet the needs of different applications.