The ERC-721 standard offers a basic interface for contracts that handle various token types. A single deployed contract may have non-fungible tokens, (e.g. un-fungible tokens). This model establishes an interface for smart contracts that may represent an unlimited number of fungible and non-fungible token kinds. Existing standards like ERC-20 mandate the use of distinct contracts for each kind of token. However, the ERC-721 standard defines the token ID as a single non-fungible index, and the collection of these non-fungibles is deployed as a single contract with global settings.