The most common token standard on Ethereum, defining how fungible tokens behave and interact with wallets and dApps.
ERC-20 (Ethereum Request for Comment 20) is the technical standard for creating fungible tokens on the Ethereum blockchain. Published in 2015 and formalized in 2017, it defines a common set of rules that all Ethereum tokens must follow — including functions for transferring tokens, checking balances, and approving third-party spending. This standardization is what makes the Ethereum ecosystem work smoothly: any ERC-20 token automatically works with every Ethereum wallet, DEX, lending protocol, and dApp. Thousands of tokens use ERC-20, from USDC and LINK to UNI and AAVE. Other token standards exist for different use cases: ERC-721 for unique NFTs, ERC-1155 for mixed fungible/non-fungible tokens, and ERC-4626 for tokenized vaults. Other chains have equivalent standards (BEP-20 on BNB Chain, SPL on Solana).
ERC-20 is the technical standard that defines how fungible tokens work on the Ethereum blockchain — establishing a common interface that all compliant tokens must implement, including functions for transferring tokens, checking balances, and approving spending on behalf of others. This standardization is what makes Ethereum's token ecosystem interoperable: any ERC-20 token automatically works with every Ethereum wallet, DEX, lending protocol, and DeFi application. Before ERC-20, each token contract had its own interface, making integration with wallets and exchanges a custom engineering effort for every single token. The standard enabled the 2017 ICO boom and continues to underpin the majority of crypto tokens. Other important Ethereum token standards include ERC-721 (non-fungible tokens/NFTs), ERC-1155 (multi-token standard), and ERC-4626 (tokenized vault standard for yield-bearing tokens). Similar standards exist on other chains: SPL tokens on Solana, BEP-20 on BNB Chain.
When Tether mints new USDT on Ethereum, it follows the ERC-20 standard — meaning the USDT automatically works in Uniswap, Aave, MetaMask, and every other Ethereum application without any integration work.
Most fungible tokens on Ethereum follow ERC-20, but not all. NFTs use ERC-721 or ERC-1155 standards. Some older tokens predate the standard and may not be fully compliant. ETH itself is not an ERC-20 token — it's the native gas token, which is why 'wrapped ETH' (WETH) exists as an ERC-20 representation.