What Is the ‘Longest Chain Rule’ in Bitcoin?

The longest chain rule, also known as the heaviest chain rule, is the core consensus mechanism that resolves conflicts when two or more valid blocks are mined at roughly the same time, creating a temporary fork. Nodes in the network are programmed to always consider and build upon the chain that has accumulated the most Proof-of-Work (the 'longest' or 'heaviest' chain).

This ensures all nodes eventually converge on a single, shared transaction history.