Order Book
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In Brief
An order book is an exchange's live list of buy and sell orders for an asset, organized by price — trades happen when a bid and an ask meet, and the book's depth shows how much buying and selling interest sits at each level.
What Is an Order Book?
An order book is an exchange's live, continuously updated list of buy and sell orders for an asset, organized by price. Buy orders (bids) line up on one side, sell orders (asks) on the other, and a trade executes whenever a bid and an ask meet. It's the core matching mechanism of traditional exchanges — and of most centralized crypto exchanges.
Reading a book tells you more than the last price: it shows how much demand and supply is actually waiting at each level.
How an Order Book Works
Traders place limit orders — "buy this much at this price or better" — which rest in the book until matched.
The highest bid and the lowest ask define the market; the gap between them is the bid-ask spread.
A market order skips the queue and fills immediately against the best resting orders, walking through the book if it's large.
The book's depth — the volume stacked near the current price — determines how much a big order moves the market.
Order Books vs. AMMs
Decentralized exchanges mostly replaced the order book with automated market makers: liquidity pools that quote prices from a formula instead of matching individual orders. Order books offer precise price control and are efficient in busy markets; AMMs offer always-on liquidity for any token without needing market makers. Both models ultimately answer the same question — at what price can this trade fill?
Order Books and Trust Wallet
Trust Wallet's built-in swap shows you a firm quote to review before you sign, whatever machinery — pools or books — produces the price behind it. Understanding order books explains what that quote means: it's the market's real, current answer for your trade size, not just the last printed price.