ERC-721 introduced the widely used Ethereum format for non-fungible tokens.
ERC-721 is an Ethereum Request for Comment standard describing an interface for unique, individually identifiable tokens. Unlike interchangeable tokens, each ERC-721 token has its own identity and can represent a digital collectible, game item, certificate, or another distinct asset.
The proposal was authored by William Entriken, Dieter Shirley, Jacob Evans, and Nastassia Sax. It became especially prominent during the growth of Ethereum-based digital collectibles in the late 2010s. The standard supports ownership tracking and transfers through compatible smart contracts.
ERC-20 is a different standard for fungible tokens, where each unit is intended to be interchangeable. ERC-1155 can represent multiple token types within one contract, including both fungible and non-fungible assets. The token standard itself does not automatically establish legal ownership of an off-chain physical item.