Permissionless blockchain (public blockchain)

On a permissionless or public blockchain there is no gatekeeper deciding who may join. Anyone can download the software, sync the full history, create addresses and broadcast transactions, and anyone who meets the economic requirements, such as buying mining hardware or staking coins, can take part in producing blocks. Bitcoin and Ethereum are the reference examples.

Openness is what gives these networks their main properties: transparent ledgers that anyone can audit, applications that can be built without a licence, and resistance to a single company or government shutting down accounts. It is also why public chains need a native token, since rewards and fees are the only way to motivate strangers to secure the system honestly.

The trade-offs are real. Every transaction is visible, throughput is limited by the need for many independent nodes to keep up, and fees rise when demand spikes. Permissionless access also means scammers and sanctioned actors can use the network, which puts pressure on validators and front-ends to filter activity.