Order book

An order book is a continuously updated list of outstanding buy and sell orders for an asset on a trading venue, organised by price. Buy orders (bids) are ranked from highest to lowest, and sell orders (asks) from lowest to highest, so the best available prices sit at the top. Each entry shows a price and the quantity offered at it.

The order book records intentions to trade; a transaction occurs only when a buy and a sell order overlap in price and are matched. A common misconception is that a full order book guarantees you can trade at the shown prices—large orders may consume several price levels at once.