ERC-20

ERC-20 (the same as EIP-20) sets a minimal common interface. The required functions are totalSupply, balanceOf, transfer, transferFrom, approve and allowance, plus the Transfer and Approval events. The optional name, symbol and decimals improve usability; decimals is usually 18, and balances are stored as integers (one token equals 10^18 base units). The approve plus transferFrom pattern, known as the allowance model, is what lets a third-party contract such as a decentralized exchange move your tokens once authorized.

It is the most widely used token standard on Ethereum and the substrate of most stablecoins, governance tokens and tokenized assets. Its common interface is what makes composable liquidity possible across protocols: any tool can read and move an ERC-20 without custom code. The standard is EIP-20, in Final status, created on 19 November 2015 by Fabian Vogelsteller and Vitalik Buterin.

The stablecoins USDC (issued by Circle) and USDT (Tether) are ERC-20, as are the governance tokens UNI (Uniswap) and AAVE (Aave) and Lido's stETH. For tokenization, ERC-20 is the base on which ERC-3643 (T-REX) layers identity verification and compliance-driven transfer control, so most fungible real-world assets are issued as ERC-20 or ERC-3643.