Definition
Block censorship is a security and neutrality risk in blockchain systems where certain transactions, addresses, or contract interactions are intentionally prevented from achieving block inclusion. It occurs when a validator, block builder, or other entity with influence over block contents selectively omits or indefinitely postpones specific transactions. This behavior can be driven by external pressure, protocol-level incentives, regulatory constraints, or strategic motives related to MEV extraction.
As a form of selective denial of service at the consensus layer, block censorship undermines the assumption that valid transactions are treated equally by the network. It can manifest as outright refusal to include targeted transactions or as persistent de-prioritization that makes their confirmation economically or practically infeasible. In severe cases, coordinated censorship by a large share of validators or block builders can compromise the effective liveness and neutrality guarantees of the chain.
Context and Usage
The term block censorship is typically used when evaluating the behavior and power of validators and block builders in modern blockchain designs. In architectures where block building and block proposing are separated, censorship risk may concentrate in specialized block builders that control transaction ordering and selection for MEV optimization. Discussions of censorship resistance focus on how easily these actors can exclude transactions and whether alternative paths to block inclusion remain available.
Block censorship is closely related to concerns about protocol-level fairness, transaction ordering, and the centralization of MEV capture. It is distinguished from ordinary prioritization by fees because it involves targeted, systematic exclusion rather than neutral economic competition for block space. The concept is central when assessing whether a blockchain maintains credible neutrality under adversarial conditions, legal constraints, or cartel-like coordination among validators and block builders.