ERC-20

What is ERC-20?

ERC-20 is a token standard on Ethereum—a shared “interface” that defines the basic functions and events a fungible token contract should expose so other apps can interact with it reliably. In practical terms, ERC-20 is why a new Ethereum token can usually be sent, received, displayed in wallets, and integrated into DeFi without every platform writing custom code for that specific token.

How Does ERC-20 Work?

ERC-20 works by specifying a common set of smart contract methods and logs (events) that external software can call or listen to. The token itself is a smart contract that maintains an internal ledger mapping addresses to balances. When you “hold” an ERC-20 token, you’re not holding coins in a separate database—your balance is a number recorded inside the token contract, associated with your Ethereum address.

At a high level, an ERC-20 token contract typically supports:

• Supply and balances: `totalSupply()` reports how many tokens exist, and `balanceOf(address)` returns how many tokens a given address owns.
• Direct transfers: `transfer(to, amount)` moves tokens from the caller’s address to another address.
• Delegated transfers (allowances): `approve(spender, amount)` sets an allowance so another address (often a dApp) can spend up to a limit, and `transferFrom(from, to, amount)` lets that approved spender move tokens on the owner’s behalf.
• Events for tracking: `Transfer` and `Approval` events are emitted so wallets, explorers, and dApps can detect activity without constantly polling state.

A step-by-step example makes the “allowance” model clearer:

1. You want to swap Token A for Token B on a decentralized exchange (DEX). 2. The DEX’s smart contract needs permission to move your Token A. 3. You call `approve(DEX_contract, 100)` on Token A, granting the DEX contract an allowance of 100 tokens. 4. When you execute the swap, the DEX contract calls `transferFrom(your_address, pool_address, amount)` to pull the approved Token A and complete the trade.

A simple analogy: ERC-20 is like a universal plug shape for token contracts. If every appliance (token) uses the same plug standard, any outlet (wallet, exchange, dApp) can support it without rewiring for each new device.

ERC-20 in Practice

ERC-20 is widely used across Ethereum’s application layer because it enables composability—protocols can “stack” together. Stablecoins such as USDC and DAI are commonly used as ERC-20 tokens in DeFi, allowing them to be deposited into lending markets, used as collateral, or traded on automated market makers.

Governance tokens are another common ERC-20 use case. Many protocols issue ERC-20 tokens that let holders vote on parameters like fee levels, collateral types, or treasury spending. Because the token follows a standard interface, governance systems, voting dashboards, and custody solutions can integrate more quickly.

ERC-20 also underpins tokenized representations of assets and positions. For example, some protocols issue ERC-20 “receipt tokens” that represent a claim on deposited funds or a share of a pool. These receipt tokens can sometimes be used elsewhere in DeFi, extending the idea of “money legos” where one protocol’s output becomes another protocol’s input.

Why ERC-20 Matters

ERC-20 matters because it dramatically reduces integration friction. Without a shared token interface, every wallet, exchange, and dApp would need bespoke support for each new token—slowing innovation and increasing the risk of implementation mistakes. Standardization makes the ecosystem more interoperable: tools like block explorers, portfolio trackers, custody systems, and DeFi protocols can support thousands of tokens with a consistent set of calls and events.

It also improves liquidity and distribution. When a token is ERC-20 compliant, it is easier to list on exchanges, add to wallets, and plug into DeFi markets—helping it reach users and enabling broader utility. While ERC-20 doesn’t guarantee a token is safe or well-designed, it provides a predictable baseline that the rest of Ethereum’s infrastructure can build around.