ERC-721

ERC-721 is a token standard on Ethereum for creating non-fungible tokens, which are tokens with unique identities rather than interchangeable units. It defines how smart contracts should mint, track, and transfer one-of-a-kind digital items. These tokens commonly power NFTs used in art, gaming, and collectibles.

Origins and authorship

ERC-721 began as an Ethereum Improvement Proposal. The specification credits William Entriken, Dieter Shirley, Jacob Evans, and Nastassia Sachs as authors. Their work formalized a shared approach so that different NFT contracts and apps could interoperate.

Name and role in Ethereum standards

ERC stands for “Ethereum Request for Comments,” the process Ethereum developers use to propose and agree on common rules. ERC-721 is the proposal that describes how non-fungible tokens should behave so apps and wallets can work with them in a consistent way

What makes ERC-721 tokens unique

Each ERC-721 token carries a unique ID and associated metadata, which lets software tell one token apart from another. The standard’s rules cover how to check who owns a token, how to transfer it, and how to approve another address to move it. Together, these rules let marketplaces and wallets interact with any compliant NFT collection.

How it differs from fungible tokens

Fungible tokens, such as those created under the ERC-20 standard, are interchangeable. One unit is equivalent to any other unit of the same token. ERC-721 assets are different because each token is distinct and cannot be swapped one for one with another token. This is why ERC-721 fits use cases where identity and scarcity matter.

Typical uses

Projects use ERC-721 to represent digital art, in-game items, metaverse parcels, and membership passes. Publishing items as NFTs enables trading and transfer on Ethereum while keeping a clear record of ownership. Some projects also explore tokenizing real-world assets to make ownership records easier to verify and transfer.

Interface basics

An ERC-721 smart contract exposes a small set of standard functions. Common actions include transferring a token, querying the current owner of a specific token ID, and granting approval so another address or marketplace contract can transfer on the owner’s behalf. Metadata fields describe things like the collection name and per-token details that apps display to users.