ERC-721, short for Ethereum Request for Comments 721, is a fundamental Ethereum token standard that underpins the creation of non-fungible tokens (NFTs).

Proposed by William Entriken, Dieter Shirley, Jacob Evans, and Nastassia Sachs in 2017, ERC-721 tokens are distinct from their fungible counterparts (such as ERC-20 tokens) in that each ERC-721 token is unique, irreplaceable, and indivisible.

ERC-721 tokens represent ownership of a specific item, collectible, or asset, and their distinctiveness characterizes them.

These tokens have been instrumental in digitizing ownership and establishing true digital scarcity, paving the way for the NFT boom that has seen art, music, virtual real estate, and other digital assets traded as unique, verifiable items.

The ERC-721 standard has enabled the development of a broad spectrum of decentralized applications (DApps) and platforms. These NFTs are used for a myriad of purposes, including digital art and media, gaming assets, virtual real estate, and authentication of physical assets.

NFTs have become a significant cultural and economic force in the crypto space, with high-profile sales and a growing ecosystem that leverages the uniqueness and provenance they provide.