The EthereumJS Monorepo, maintained by the Ethereum Foundation JavaScript team, compiles essential protocol building blocks for Ethereum’s blockchain execution layer, implemented in TypeScript for Node.js and browser environments. It includes a comprehensive suite of libraries such as Ethereum Virtual Machine (EVM), transaction, block, blockchain structures, Merkle Patricia Tree (MPT), devp2p execution networking, and is unified by the Common library for chain specifics and hardfork management. Complementary tools like RLP for encoding/decoding and Util for various helper functions enhance functionality. The EthereumJS Execution Client supports testing, research, and developer engagement with the protocol. This monorepo actively collaborates with the ChainSafe Lodestar for Ethereum Consensus Client implementation, serving as a versatile tool in the Ethereum ecosystem with clear maintenance and development branch strategies, all majorly licensed under MPL-2.0.