ERC-271

ERC-721 is the Ethereum token standard used to create non-fungible tokens (NFTs) — unique digital assets where no two tokens are identical. In contrast to ERC-20, which defines fungible tokens where every unit is interchangeable with any other, ERC-721 tokens each carry a unique identifier that makes them distinct from one another. This property makes them well-suited for representing ownership of one-of-a-kind items such as digital art, collectibles, gaming items, and real-world assets.

The most well-known early example of an ERC-721 application is CryptoKitties, a blockchain-based game where players collect, breed, and trade unique digital cats, each represented as an ERC-721 token with distinct attributes. The success of CryptoKitties in 2017 demonstrated the potential of the NFT concept and helped drive the later boom in digital art and collectibles. Since then, the ERC-721 standard has become the foundation for a vast ecosystem of NFT projects across gaming, art, music, sports memorabilia, and virtual real estate.

For traders and developers working in the NFT space, understanding ERC-721 mechanics is essential. Unlike fungible tokens, NFTs cannot be split or aggregated — you own whole tokens, each with its own unique metadata and provenance recorded on the blockchain. Marketplaces like OpenSea facilitate the buying and selling of ERC-721 tokens, and the standard is widely supported across wallets, explorers, and developer tools. A related standard, ERC-1155, extends the concept further by allowing a single contract to manage both fungible and non-fungible tokens simultaneously.