Protocols and algorithms for blockchain technology is a critical research area that focuses on the design, analysis, and optimization of the underlying mechanisms that govern decentralized networks. This includes consensus algorithms (e.g., Proof of Work, Proof of Stake, Practical Byzantine Fault Tolerance, Delegated Proof of Stake), transaction validation protocols, cryptographic techniques, sharding, and cross-chain interoperability protocols. Early research emphasized security, immutability, and decentralized consensus for cryptocurrencies like Bitcoin, while recent studies explore energy-efficient consensus, scalability, low-latency transaction processing, and robustness against adversarial attacks. Algorithmic research also addresses smart contract execution, incentive mechanisms, fault tolerance, and privacy-preserving computations using zero-knowledge proofs and homomorphic encryption. Applications span financial systems, supply chain management, healthcare, IoT integration, and decentralized governance. Current research continues to investigate hybrid and adaptive protocols, multi-layer architectures, algorithmic fairness, and performance optimization, establishing robust and efficient blockchain networks suitable for diverse industrial and enterprise applications.