# ERC-721 NFTs: the token, its metadata and what ownership means ERC-721 defines an interface for individually distinguishable tokens. The contract and token ID identify a token, and its ownership record names an account. Images and descriptions can be linked metadata. The standard does not itself establish copyright, authenticity, permanent file availability or the rights to a physical item. Evidence: [ERC-721: Non-Fungible Token Standard](https://raw.githubusercontent.com/ethereum/ERCs/583335b7912e51b1ea515bb662532dd29b27e786/ERCS/erc-721.md); [Introduction to smart contracts](https://raw.githubusercontent.com/ethereum/ethereum-org-website/dcc900ff125891da5b6c723b905a7113cf1bd864/public/content/developers/docs/smart-contracts/index.md) Canonical: https://degreesofsatoshi.com/encyclopedia/erc-721-nfts/ Published: 2026-10-02 Substantively modified: 2026-10-02 Independently verified by an automated reviewer: 2026-10-02T15:10:23.134Z AI-assisted research and drafting with a separate automated source-verification pass; no external expert or named human review is implied. ## Key facts - **Identity:** Token ID within a particular contract and network ([ERC-721: Non-Fungible Token Standard](https://raw.githubusercontent.com/ethereum/ERCs/583335b7912e51b1ea515bb662532dd29b27e786/ERCS/erc-721.md)) - **Ownership lookup:** ownerOf names the owning account ([ERC-721: Non-Fungible Token Standard](https://raw.githubusercontent.com/ethereum/ERCs/583335b7912e51b1ea515bb662532dd29b27e786/ERCS/erc-721.md)) - **Metadata:** Optional interface may return a token URI ([ERC-721: Non-Fungible Token Standard](https://raw.githubusercontent.com/ethereum/ERCs/583335b7912e51b1ea515bb662532dd29b27e786/ERCS/erc-721.md)) ## A token ID makes each item separately trackable An ERC-20 balance can say an account holds five interchangeable units. ERC-721 instead tracks which account owns a particular token ID. A single contract can hold an entire collection of those distinct records. The ID is not globally unique. Token 42 in one collection and token 42 in another are different records. A complete identifier includes the network and contract as well as the number. Evidence: [ERC-721: Non-Fungible Token Standard](https://raw.githubusercontent.com/ethereum/ERCs/583335b7912e51b1ea515bb662532dd29b27e786/ERCS/erc-721.md); [ERC-20: Token Standard](https://raw.githubusercontent.com/ethereum/ERCs/583335b7912e51b1ea515bb662532dd29b27e786/ERCS/erc-20.md) ## Example: transferring token 42 changes a record, not a file Imagine a collection where token 42 belongs to account A. A valid transfer to account B updates the ownership record and emits a transfer event. A wallet can query ownerOf to display the new owner. The image might still be fetched from a separate URI. Transferring the token does not necessarily copy a file, remove anyone else’s copy or change the terms under which that image may be used. Evidence: [ERC-721: Non-Fungible Token Standard](https://raw.githubusercontent.com/ethereum/ERCs/583335b7912e51b1ea515bb662532dd29b27e786/ERCS/erc-721.md); [Interacting with smart contracts](https://raw.githubusercontent.com/ethereum/ethereum-org-website/dcc900ff125891da5b6c723b905a7113cf1bd864/public/content/developers/docs/smart-contracts/interacting/index.md) ## Metadata points outward; the standard does not resolve every promise The optional metadata extension can provide a name, description and image reference. Where those bytes live, who can update them and whether they remain retrievable are properties of the actual project. Likewise, a claim about copyright or a physical asset needs its own evidence and terms. The token interface supplies technical ownership operations; it does not verify an artist’s identity or a warehouse’s inventory. Evidence: [ERC-721: Non-Fungible Token Standard](https://raw.githubusercontent.com/ethereum/ERCs/583335b7912e51b1ea515bb662532dd29b27e786/ERCS/erc-721.md); [Introduction to smart contracts](https://raw.githubusercontent.com/ethereum/ethereum-org-website/dcc900ff125891da5b6c723b905a7113cf1bd864/public/content/developers/docs/smart-contracts/index.md) ## A single-token approval and an operator approval differ ERC-721 provides approval for a particular token and approval-for-all for an operator over the owner’s tokens in that contract. A marketplace interaction can therefore request a broader permission than one transfer. Safe transfer methods check whether a contract recipient implements the expected receiving interface. This reduces one type of accidental incompatibility; it does not certify that the recipient or marketplace is trustworthy. Evidence: [ERC-721: Non-Fungible Token Standard](https://raw.githubusercontent.com/ethereum/ERCs/583335b7912e51b1ea515bb662532dd29b27e786/ERCS/erc-721.md); [Interacting with smart contracts](https://raw.githubusercontent.com/ethereum/ethereum-org-website/dcc900ff125891da5b6c723b905a7113cf1bd864/public/content/developers/docs/smart-contracts/interacting/index.md) ## Questions ### Does buying an NFT automatically transfer copyright? The ERC-721 standard does not define copyright licensing. Any such rights depend on separate terms and the authority of whoever grants them. Evidence: [ERC-721: Non-Fungible Token Standard](https://raw.githubusercontent.com/ethereum/ERCs/583335b7912e51b1ea515bb662532dd29b27e786/ERCS/erc-721.md) ### Is the image always stored directly on Ethereum? No. The metadata interface can return a URI. A specific project may store data onchain or elsewhere, with different persistence and update properties. Evidence: [ERC-721: Non-Fungible Token Standard](https://raw.githubusercontent.com/ethereum/ERCs/583335b7912e51b1ea515bb662532dd29b27e786/ERCS/erc-721.md) ### Can two collections both have token number 42? Yes. Token IDs are scoped to a contract. The collection’s contract and network are needed to distinguish the records. Evidence: [ERC-721: Non-Fungible Token Standard](https://raw.githubusercontent.com/ethereum/ERCs/583335b7912e51b1ea515bb662532dd29b27e786/ERCS/erc-721.md) ## Claims and scope ### erc-721-nfts-quick-answer ERC-721 defines an interface for individually distinguishable tokens. The contract and token ID identify a token, and its ownership record names an account. Images and descriptions can be linked metadata. The standard does not itself establish copyright, authenticity, permanent file availability or the rights to a physical item. Scope: {"collection":"ethereum","dataAsOf":null,"blockHeight":null} ### erc-721-nfts-fact-identity Identity: Token ID within a particular contract and network Scope: {"collection":"ethereum","dataAsOf":null,"blockHeight":null} ### erc-721-nfts-fact-ownership-lookup Ownership lookup: ownerOf names the owning account Scope: {"collection":"ethereum","dataAsOf":null,"blockHeight":null} ### erc-721-nfts-fact-metadata Metadata: Optional interface may return a token URI Scope: {"collection":"ethereum","dataAsOf":null,"blockHeight":null} ## Sources - [ERC-721: Non-Fungible Token Standard](https://raw.githubusercontent.com/ethereum/ERCs/583335b7912e51b1ea515bb662532dd29b27e786/ERCS/erc-721.md) — Ethereum Request for Comments. Defines token-specific ownership, transfer approvals, metadata pointers and receiving-contract checks. Locator: Specification; metadata extension; transfer and operator methods. Retrieved: 2026-10-02T14:35:55.241155+00:00. - [Introduction to smart contracts](https://raw.githubusercontent.com/ethereum/ethereum-org-website/dcc900ff125891da5b6c723b905a7113cf1bd864/public/content/developers/docs/smart-contracts/index.md) — ethereum.org contributors. Supports contract code/state, deterministic rules, illustrative vending logic, external-data limits and multisignature access. Locator: What is a smart contract; a digital vending machine; limitations; multisig. Retrieved: 2026-10-02T14:35:40.398357+00:00. - [ERC-20: Token Standard](https://raw.githubusercontent.com/ethereum/ERCs/583335b7912e51b1ea515bb662532dd29b27e786/ERCS/erc-20.md) — Ethereum Request for Comments. Defines fungible token balances, optional display metadata and spending allowance behavior. Locator: Methods: decimals, balanceOf, transfer, approve, transferFrom, allowance. Retrieved: 2026-10-02T14:35:55.037727+00:00. - [Interacting with smart contracts](https://raw.githubusercontent.com/ethereum/ethereum-org-website/dcc900ff125891da5b6c723b905a7113cf1bd864/public/content/developers/docs/smart-contracts/interacting/index.md) — ethereum.org contributors. Supports read-only calls, state-changing transactions, ABI decoding and limits of simulation. Locator: Reading; writing; understanding contract ABIs; events and logs; simulating. Retrieved: 2026-10-02T14:35:40.398262+00:00. ## Revision history - 2026-10-02: First publication after primary-source research and independent automated verification. ## Cite this entry Degrees of Satoshi editorial project. “ERC-721 NFTs: the token, its metadata and what ownership means.” Published 2026-10-02; updated 2026-10-02. https://degreesofsatoshi.com/encyclopedia/erc-721-nfts/