ERC-721 (Ethereum Request for Comments 721)

ERC-721 is a standard defining non-fungible tokens (NFTs) on the Ethereum blockchain. Unlike the interchangeable ERC-20 tokens, each ERC-721 token is unique and has its own identifier, making it ideal for creating and managing collectible digital assets.

Key features of ERC-721:

1. Uniqueness: Each token has a unique identifier.
2. Non-fungibility: One token cannot be replaced by another.
3. Applications: Used for creating NFTs — digital art, in-game assets, collectibles, and more.
4. Ownership and transfer: The standard includes functions for managing ownership rights and transferring tokens between users.

Examples of use:

• Collectibles: CryptoKitties, Axie Infinity.
• Digital art: NFT platforms like OpenSea use ERC-721 to manage digital assets.

This standard supports a variety of business models and has become the foundation for the rapid growth of the NFT market.