Overview
A fork choice rule is the algorithm a blockchain uses to decide which competing chain is canonical when forks occur. It determines how nodes agree on a single history. Different protocols use different rules.
How It Works
Bitcoin uses the longest chain rule, favoring the chain with the most accumulated work. Ethereum uses LMD-GHOST, which tracks attestations from validators. The rule lets all nodes independently converge on the same chain.
Why It Matters
The fork choice rule is central to chain safety and liveness. A flawed rule can allow attacks or cause persistent disagreements. It is one of the most important design choices in a blockchain protocol.
Related Concepts
Fork Choice Rules relate to the Longest Chain Rule, Finality, and Consensus. They define how a chain selects between competing branches.