Permissioned and permissionless blockchain models are a central research focus that examines how different consensus and governance structures impact scalability, security, and decentralization in blockchain ecosystems. Research papers in this area compare permissionless models—such as Bitcoin and Ethereum, where anyone can join, validate, and participate—with permissioned models, such as Hyperledger Fabric and Corda, which restrict participation to trusted entities with controlled access. Studies highlight trade-offs between the decentralization and transparency of permissionless systems versus the efficiency, privacy, and regulatory compliance of permissioned systems. Recent works explore hybrid models that integrate the strengths of both, enabling scalability while maintaining selective transparency and trust. Consensus mechanisms such as Proof of Work (PoW), Proof of Stake (PoS), Byzantine Fault Tolerance (BFT), and Delegated Proof of Stake (DPoS) are analyzed in terms of performance, energy efficiency, and applicability in permissioned versus permissionless settings. Applications range from financial services, supply chain management, and healthcare to IoT, where the choice of blockchain model depends on trust, security, and performance requirements. Overall, research in permissioned and permissionless blockchain models provides a foundation for designing adaptable blockchain ecosystems that balance openness, security, and efficiency for diverse application domains.