Blockchain Glossary

Longest Chain

The chain of blocks that prevails in the case of a fork (see “Fork”, above.) When miners “chain” a new block to the previous one, the way the blocks are “chained” has a value. The harder the work done in chaining a block (in PoW blockchains), or the closest a block complies to the consensus rules, the higher the score is for that piece of the chain. In the event of a fork, when a node has more than one new block or blockchain to choose from to update itself, the node calculates the cumulative “score” generated when creating each chain, and chooses the chain with the highest score (in Proof of Work this “score” is referred as “difficulty”, and the chain with the highest cumulative difficulty is the chosen one.) In this way, nodes in a P2P network can reach the same decision without communicating with each other, but simply using the same algorithm to evaluate the options presented to them.