Permissionless Blockchains or Public Blockchains are fully decentralized platforms where any anonymous user can participate in the consensus mechanism and data validation process. Permissioned Blockchains (Private Blockchains), on the other hand, are partially decentralized networks where only authorized users can participate. The degree of decentralization in Permissioned Blockchain networks varies based on the requirement of the governing entity or entities. So, while any user can add nodes to a Public Blockchain, only pre-authorized users can add nodes to a Private Blockchain.