Currency is any widely accepted medium of exchange, unit of account, and store of value. It is the foundational abstraction that makes trade possible – without it, every transaction requires a direct barter of goods or services.

Forms of currency#

Commodity money#

The earliest currencies were physical commodities with intrinsic value – gold, silver, salt, cattle. These worked because they were scarce, durable, and widely recognized, but they were heavy to transport and impractical to divide precisely.

Fiat currency#

Modern economies run on fiat currency – money issued by a government that is not backed by a physical commodity. The US Dollar, Euro, and Japanese Yen are fiat currencies. Their value rests on trust in the issuing government and the legal obligation to accept them for debts (legal tender laws). Central banks manage the money supply, set interest rates, and act as lenders of last resort.

Digital currency#

Digital currency exists only in electronic form. This is a broad category that includes bank balances (most “money” today is already digital entries in bank ledgers), mobile payment systems, and cryptocurrency.

What makes something function as currency#

For any asset to work as currency, it needs several properties:

  • Fungibility – one unit is interchangeable with any other unit of the same denomination.
  • Divisibility – it can be broken into smaller units for transactions of varying sizes.
  • Durability – it does not degrade with use or over time.
  • Portability – it is easy to transfer between parties.
  • Scarcity – the supply is limited or controlled enough to maintain value.
  • Acceptability – participants in the economy recognize and accept it.

Cryptocurrency as currency#

Cryptocurrency introduces a new form of digital currency built on blockchain technology. Rather than relying on a central bank, cryptocurrencies use cryptographic proofs and consensus mechanisms to control issuance and verify transfers.

In practice, most cryptocurrencies behave more like speculative assets than day-to-day currencies – their volatility makes them unreliable as a unit of account. Stablecoins address this by pegging their value to a fiat currency (typically USD), combining the programmability of crypto with the price stability needed for everyday use. USDC, USDT, and DAI are the most widely circulated stablecoins in DeFi.

On Ethereum, fungible tokens follow the ERC-20 standard, which defines a common interface for transfer, approval, and balance queries. This standardization is what makes tokens composable across DEXs, lending protocols, and liquidity pools.

Currency in DeFi#

In the DeFi ecosystem, the concept of currency extends to any fungible token that a protocol accepts. This includes:

  • Stablecoins – used as the base pair in most trading pools and as collateral in lending protocols.
  • Native chain tokens (ETH, SOL, AVAX) – used to pay gas fees and often serve as collateral or trading pairs.
  • Governance tokens – while primarily used for DAO voting, they trade freely and are often used as collateral.
  • Liquidity pool tokens – receipts issued when providing liquidity to an AMM. These are fungible, tradeable, and can themselves be staked in yield farming strategies.
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