In the context of blockchains, 'permissioned' and 'permissionless' refer to the degree of access control and governance within the network. Permissioned blockchains require participants to obtain permission to join, and they often have a central authority that oversees the network, making it more suitable for businesses or organizations that require privacy and regulatory compliance. On the other hand, permissionless blockchains allow anyone to participate without any restrictions, promoting decentralized control and transparency. Bitcoin and Ethereum are examples of permissionless blockchains, while Hyperledger and R3 Corda illustrate permissioned blockchains. These differences influence not only the access and security of data but also the level of decentralization and the consensus mechanisms employed in each type of blockchain.