Ethereum Token Standards Explained: ERC-20, ERC-721 and ERC-1155

Ethereum token standards are agreed-upon sets of rules that allow smart contracts to create and manage digital assets in a predictable way. By standardizing functions like transferring tokens or checking balances, these frameworks ensure that wallets, exchanges, and decentralized applications can interact with thousands of different tokens without needing custom code for each one. The three most widely used standards are ERC-20 for fungible tokens, ERC-721 for non-fungible tokens, and ERC-1155 for multi-token contracts.

The Foundation of Tokens: ERC-20

Introduced in 2015, the ERC-20 standard defines the rules for fungible tokens. Fungibility means that every unit of the token is identical in value and utility to every other unit, much like a US dollar. This standard is the underlying architecture for most stablecoins, governance tokens, and utility tokens on the Ethereum network.

An ERC-20 contract is essentially a decentralized spreadsheet. It maps user addresses to token balances. When a user transfers an ERC-20 token, they are not sending a file; they are instructing the smart contract to deduct a specific amount from their balance and add it to another address's balance. The core functions include balanceOf to check holdings, transfer to move tokens directly, and a combination of approve and transferFrom which allows third-party smart contracts to move tokens on a user's behalf.

For example, if a user wants to swap 100 $USDC on a decentralized exchange, they first call approve, granting the exchange contract permission to move 100 USDC. The exchange then calls transferFrom to execute the trade. If gas costs for executing a transaction are 30 gwei, the total network fee paid in Ethereum ($ETH) depends on the computational complexity of the contract, meaning a simple transfer costs less than a complex swap. Network fees fluctuate based on network demand.

Uniqueness and Ownership: ERC-721

The ERC-721 standard was finalized in 2018 to handle non-fungible tokens. Non-fungibility means each token has a unique identifier and cannot be interchanged on a one-to-one basis with another token in the same contract. This standard is used for digital art, real estate representations, and identity credentials.

Unlike ERC-20, where the contract tracks a single total balance per user, an ERC-721 contract tracks the specific ownership of individual token IDs. The core functions are similar in naming but operate differently. The ownerOf function returns the address holding a specific token ID. The transferFrom function moves a specific token ID rather than an amount. Because each token is distinct, the standard also includes metadata extensions, allowing the contract to point to off-chain data like images or attributes via a Uniform Resource Identifier.

The Multi-Token Standard: ERC-1155

Developed to address inefficiencies in previous standards, ERC-1155 is a multi-token standard that allows a single smart contract to manage infinite types of both fungible and non-fungible tokens. This was initially driven by the gaming sector, where a game might require thousands of unique items (ERC-721) alongside a fungible in-game currency (ERC-20).

Under older standards, deploying a new token type requires deploying a new smart contract, which incurs significant network fees. ERC-1155 combines multiple token types into a single contract and introduces batch transfer functions. A user can transfer multiple different token types to an address in a single transaction, significantly reducing network fees and congestion. The balanceOf function in ERC-1155 requires both an address and a token ID, returning the quantity of that specific ID owned by the user.

Common Misconceptions

• Tokens live in wallets: Tokens do not reside in user wallets. They exist only as data entries within the smart contract on the blockchain. Wallets merely read the blockchain to display balances and hold the private keys necessary to authorize changes to the contract.
• Standard implies safety: Adhering to an ERC standard only guarantees that a token has a specific set of functions. It does not mean the smart contract is free of bugs, backdoors, or malicious code designed to freeze user funds.
• Approvals expire: When a user calls the approve function to allow a decentralized application to spend their tokens, that approval typically persists until the user explicitly revokes it by sending a new transaction setting the approval amount to zero.

How This Connects to the Market

The standardization of tokens is the primary driver of interoperability in decentralized finance. Because exchanges and lending protocols know exactly how to interface with ERC-20 and ERC-721 contracts, developers can launch new assets that are immediately compatible with global financial infrastructure. As decentralized finance matures, the evolution of these standards continues to shape market dynamics, influencing everything from the technical overhead of launching new projects to the mechanics of Coins vs Tokens: ERC-20, SPL and What the Difference Means. Market participants monitor standard upgrades because they often reduce friction, lower transaction costs, and enable more complex financial instruments on-chain.