The Ethereum Yellow Paper repository contains the canonical formal specification of the Ethereum protocol, describing its consensus rules, virtual machine (EVM) semantics, transaction formats, and state transition logic. It encodes rigorous mathematics and pseudocode defining how blocks are validated, how world state evolves, gas accounting, account balances, and execution semantics of opcodes. The paper is the authoritative technical reference for clients, protocol architects, and researchers seeking a precise, unambiguous description of Ethereum’s design and expected behavior. The repository may include the LaTeX source, historical versions (by hard fork), comments, errata, and supplemental updates as the protocol evolves. Because Ethereum has had multiple upgrades (e.g. “Byzantium”, “Istanbul”, “Berlin”), the Yellow Paper often tracks changes to opcode gas costs, state transition nuance, and new EIPs.