> ## Documentation Index
> Fetch the complete documentation index at: https://docs.theblockchainlibrary.com/llms.txt
> Use this file to discover all available pages before exploring further.

# ERC-721

> ERC-721 is the standard for non-fungible tokens (NFTs) on the Ethereum blockchain. Unlike ERC-20 tokens, which are interchangeable, every ERC-721 token is unique and distinct, identified by a specific 'Token ID' within a smart contract. This standard allows developers to track, o

# ERC-721

ERC-721 is the standard for non-fungible tokens (NFTs) on the Ethereum blockchain. Unlike ERC-20 tokens, which are interchangeable, every ERC-721 token is unique and distinct, identified by a specific 'Token ID' within a smart contract. This standard allows developers to track, own, and transfer unique digital items such as artwork, collectibles, or digital identity assets. By providing a uniform interface, it enables marketplaces like OpenSea to support an infinite variety of distinct items using a single architecture.

## Definition

ERC-721 is the standard for non-fungible tokens (NFTs) on the Ethereum blockchain. Unlike ERC-20 tokens, which are interchangeable, every ERC-721 token is unique and distinct, identified by a specific 'Token ID' within a smart contract. This standard allows developers to track, own, and transfer unique digital items such as artwork, collectibles, or digital identity assets. By providing a uniform interface, it enables marketplaces like OpenSea to support an infinite variety of distinct items using a single architecture.

## Simple explanation

ERC-721 is for items that are one-of-a-kind. Think of it like a trading card game where every card has a unique serial number. Unlike coins in your pocket that are all the same, these tokens are unique and cannot be swapped one-for-one.

## Why it matters

It created the digital collectibles and NFT market. It allows for provable scarcity and ownership of unique digital property.

## How it works

Similar to ERC-20, it uses a smart contract interface, but it maps a unique `tokenId` to a specific owner address. It includes functions to transfer ownership of a specific item and query who owns a specific unique asset. The metadata associated with the token can point to off-chain data like images or descriptions.

## Real-world example

CryptoPunks and Bored Ape Yacht Club are iconic collections built on the ERC-721 standard.

## Advantages

* Verifiable digital ownership
* Unique asset representation
* Interoperable with NFT marketplaces

## Limitations

* High gas for minting
* Data storage scalability

## Common misconceptions

* People think all NFTs must be pictures, but they can be any digital identity or asset.
* Many believe NFTs themselves are stored on-chain, but often only the metadata reference is.

## Related knowledge

* [Smart Contract](/generated/v2/glossary/smart-contract) — term

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**Canonical knowledge ID:** `glossary:erc-721`