Euler is a modular lending protocol that lets users lend and borrow crypto assets through ERC-4626 credit vaults. The Euler Vault Kit constructs isolated lending vaults, each holding a single underlying token and enforcing its own interest model, risk limits and collateral rules. The Ethereum Vault Connector links vaults into a unified account, mediates solvency checks and supports features like batching, sub-accounts and operators. On top of these vaults, Euler Earn vaults aggregate strategies for passive depositors by allocating funds across selected lending markets within the Euler ecosystem.