ERC-721 is Ethereum's prevailing non-fungible token standard. ERC-721 tokens have standardized functions within their smart contracts, which include inter-account transferrability, token balance querying, and approvability for third-party spending.
ERC-721 provides a common token creation framework for non-fungible tokens on Ethereum Virtual Machine (EVM)-based blockchains. It was first proposed by William Entriken, Dieter Shirley, Jacob Evans, and Natassia Sachs in 2018. The interface standard's requirements for compliant non-fungible token smart contracts include all of the interfaces for the ERC-165 token standard, as well as: 'BalanceOf', 'safeTransferFrom', 'TransferFrom', 'Approve', 'SetApproveForAll', 'getApproved', 'isApprovedForAll', 'Transfer', 'ApprovalForAll', 'owenerOf'and 'Approval'.