Soulbound token (SBT)

The term was popularized by Vitalik Buterin in a January 2022 blog post, with a name taken from the soulbound items in the video game World of Warcraft. The foundational paper, Decentralized Society: Finding Web3's Soul, by E. Glen Weyl, Puja Ohlhaver and Vitalik Buterin, was published in May 2022 and introduced SBTs as a primitive for a decentralized society. There is no single canonical standard. ERC-5192 (Minimal Soulbound NFTs) is final and the most adopted: it extends ERC-721, adds a locked(tokenId) view and reverts transfer functions when the token is locked. EIP-4973 remains a draft.

It enables verifiable identity and reputation without a secondary market. If a credential cannot be bought, its value as proof holds. On the compliance side, SBTs fit KYC verification, proof of attendance, qualifications, governance resistant to vote buying and on-chain reputation for undercollateralized lending. ERC-5192 also lets the owner burn the token to remove credentials they no longer wish to keep, which gives control to the holder.

POAP, the Proof of Attendance Protocol, issues event attendance badges and is a conceptual precursor of the SBT, even if it does not strictly follow an SBT standard. The Binance Account Bound (BAB) token, launched in 2022 on BNB Chain, works as a KYC verification SBT. Gitcoin Passport aggregates credentials and identity to resist sybil attacks, showing the SBT as a reputation layer.