ERC-721

Overview

Meaning and scope

ERC-721 is the Ethereum interface standard for non-fungible tokens, defining common functions and events for identifying unique token IDs, checking ownership, granting approvals, and transferring NFTs. NFT ownership identifies control of a token under a specific contract or protocol; it does not automatically transfer copyright, physical title, service performance, or other off-chain rights.

How it works

The standard defines an interface, not a guarantee of metadata quality, scarcity, royalties, security, or legal rights. Individual contracts may add minting, pausing, upgradeability, enumeration, or custom transfer logic. Operationally, integrators verify the chain and contract, ERC-165 support, ownerOf and transfer behavior, approvals, safe receiver checks, metadata URI handling, events, proxy implementation, and collection-specific extensions. Smart-contract defects, misleading metadata, unauthorized minting, marketplace impersonation, illiquid markets, custody mistakes, and uncertainty over off-chain rights can reduce or eliminate practical value. For custody or marketplace support, verify chain, canonical contract or collection, token ID, ownership, approvals, metadata source, transfer behavior, royalties, and off-chain terms.

Operational checks and limits

ERC-721 defines a standard Ethereum interface for individually identified non-fungible tokens. Ownership, approval and safe-transfer semantics depend on the standard and the particular implementation.

Practical example

A ticket issuer assigns a unique token ID to each event ticket and transfers ownership under its contract’s controls.

Distinctions

ERC-721 emphasizes unique token identities; ERC-1155 supports multiple token IDs and quantities in one contract.

How to evaluate it

The token standard describes interfaces or transfer semantics, not the economic value or authenticity of an item; when integrating ERC-721, verify the contract and network before reading metadata, ownership, or transfer events. When evaluating ERC-721, test approvals, receiving contracts, batch behavior where relevant, and token IDs; a marketplace display should not be treated as proof of transferable rights or of off-chain asset ownership. Related concepts: ERC-1155; NFT Collection; NFT Minting.