automated market maker (AMM)

An automated market maker is a smart contract that lets people trade one token for another instantly, by trading against a shared pool of funds rather than waiting for a matching buyer or seller. Traditional exchanges run an order book: your order to sell sits in a list until someone wants to buy at your price. An AMM throws out the waiting room entirely. There is always a counterparty, because you are swapping with a pool of two tokens, and a formula sets the price on the spot.

The clever part is that formula. A common one keeps the product of the two token amounts in the pool constant — if the pool holds, say, apples and oranges, then apples × oranges must stay the same after every trade. When you take apples out, you must put oranges in, and because the leftover apples are now scarcer, each one costs more oranges than the last. The pool prices itself automatically: the more of something you buy, the steeper the price climbs, with no human quoting it. This self-balancing math is why an AMM never needs to be told what anything is worth.

AMMs matter because they made trading possible for any token, anywhere, without a company in the middle matching trades or holding your money. Anyone can create a market for a new token by seeding a pool, and anyone can trade against it a second later. This is the engine under most decentralized exchanges, and it turned market-making — once the job of specialized firms — into something an ordinary person can take part in just by adding funds to a pool.