What Is Order Book?
The order book is the central data structure of any exchange: a live list of every unfilled limit order, organized by price. Buy orders (bids) on one side, sell orders (asks) on the other. The highest bid and lowest ask define the current spread.
The depth of the book — how much volume sits at each price level — reveals supply and demand. A 'thin' book means small orders can move price significantly. A 'thick' book at certain levels often acts as support or resistance because large orders absorb buying or selling pressure.
On equity exchanges, full order-book visibility (Level 2) usually requires a paid data subscription. On crypto exchanges, full order books are public. Reading the book is a skill — recognizing fake walls, spoofing, and genuine accumulation takes practice.
Related terms
- Bid-Ask Spread — The gap between the highest price buyers will pay (bid) and the lowest price sellers will accept (ask).
- Liquidity — The ease with which an asset can be bought or sold without significantly affecting its price.
- Market Maker — Firm that quotes both buy and sell prices, providing liquidity for a profit on the spread.
- Limit Order — An order to buy or sell at a specified price or better — guarantees price, not execution.