ERC-721 is a technical token standard on Ethereum that defines how non-fungible tokens (NFTs) are created, tracked, owned, and transferred. Unlike fungible tokens where every unit is interchangeable, an ERC-721 token is unique, so each token can represent a distinct item, right down to its specific identifier.
How ERC-721 works on Ethereum
ERC-721 is implemented in a smart contract, which acts as a rulebook for NFT ownership. Each NFT is identified by a token ID, and the contract maintains a record of which wallet address owns each token. The standard also defines common functions for transferring tokens and for checking balances and ownership, which helps wallets, marketplaces, and other apps interact with NFTs in a consistent way.
A key feature is that ERC-721 tokens can reference metadata, usually via a token URI. This metadata can describe the asset, such as a name, traits, or a link to media like an image or video. While the ownership record lives on-chain, the media itself is often stored off-chain (for example, on IPFS or traditional servers), which is why the reliability of metadata hosting matters.
Real-world uses and why it differs from ERC-20
ERC-721 is widely used for digital art collectibles, in-game items, event tickets, and membership passes, any scenario where individuality matters. For example, two NFTs from the same collection may have different attributes, making them distinct even if they look similar.
Compared with ERC-20, which is designed for interchangeable units like currencies, ERC-721 enables provable uniqueness and clear ownership history. This matters in crypto because standardization makes NFTs portable across the Ethereum ecosystem, reducing integration friction and supporting more transparent digital ownership.