An order book is a real-time electronic list showing all current buy and sell orders for a specific trading pair on an exchange. It lists the prices traders are willing to buy and sell at, helping the market set the next trade price.
Order books typically have two columns: bids and asks. Bids are buy offers and appear at the top when buyers compete. Asks are sell offers and show up when sellers set their lowest prices. Most platforms also display the total order size at each price and often use green for buys and red for sells. This setup helps traders quickly spot where demand and supply are strongest.
Order books mainly contain two types of orders. Limit orders set a specific price and wait for someone to match them. Market orders aim to trade immediately at the best available price and do not stay in the book. Most of the book is made up of limit orders, while market orders fill those limits and result in trades. Many exchanges also show a brief history of recent trades for reference.
Exchanges use a matching engine to pair buy and sell orders. When a market order comes in, the engine matches it with the best available limit orders until the full amount is traded. The way the order book is set up affects how easily large orders can be filled without causing big price changes. This is known as market depth.
The spread is the gap between the highest bid and the lowest ask. A small spread usually means there are many buyers and sellers with similar prices, making trading cheaper and quicker. If there are few orders or large gaps between prices, trades can move the market more, causing extra slippage for large market orders.
Traders use order books to find possible support or resistance levels, estimate how much an order might move the price, and decide when to enter or exit trades. Market makers place many small limit orders to profit from the spread. Watching changes in the order book can also reveal short-term market sentiment.
Order books show traders’ intentions, not completed trades, so they can sometimes be misleading. Some people place fake orders to make it look like there is more interest, then cancel them before they are filled. This can distort the real supply or demand and mislead other traders. Sudden market orders can also clear out several price levels and cause sharp price changes, which is why it’s important to watch the book’s depth.
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