A decentralized exchange, or DEX, is a trading platform that holds no assets in custody, employs no order book in the traditional sense, and requires no registration from its users. It executes trades directly from pooled liquidity through a smart contract, and the mechanism by which it prices assets is encoded in mathematics rather than determined by a counterparty.

The central innovation enabling DEXes is the automated market maker, or AMM. In a traditional exchange — including a centralized crypto exchange — buyers and sellers are matched based on the quantities and prices at which they are willing to transact, recorded in a central order book. An AMM eliminates the order book entirely. Instead, it manages a liquidity pool: a smart contract holding two assets in a trading pair, into which liquidity providers deposit equal values of both assets. Users trade directly against the pool, depositing one asset and withdrawing the other, with the price determined by the ratio of the two assets in the pool at the time of the trade.