Blockchain networks can differ in who can participate and who has access to the data. Networks are typically described as either public or private, depending on who is allowed to participate, and permissioned or permissionless, depending on how participants gain access to the network.
Public and private blockchains
Public blockchain networks typically allow anyone to join and for participants to remain anonymous. A public blockchain uses internet-connected computers to validate transactions and achieve consensus. Bitcoin is probably the most well-known example of a public blockchain, and it achieves consensus through "bitcoin mining." Computers on the bitcoin network, or 'miners,' try to solve a complex cryptographic problem to create proof of work and thereby validate the transaction. Outside of public keys, there are few identity and access controls in this type of network.
Private blockchains use identity to confirm membership and access privileges and typically only permit known organizations to join. Together, the organizations form a private, members-only "business network." A private blockchain in a permissioned network achieves consensus through a process called "selective endorsement," where known users verify the transactions. Only members with special access and permissions can maintain the transaction ledger. This network type requires more identity and access controls.
When building a blockchain application, it’s critical to assess which type of network will best suit your business goals. Private and permissioned networks can be tightly controlled and preferable for compliance and regulatory reasons. However, public and permissionless networks can achieve greater decentralization and distribution.