Orderboken

Orderboken, or the order book, is a real-time electronic register of outstanding buy and sell orders for a security or instrument on an exchange. It is organized by price level and displays the quantities available at each price on both sides of the market (bids and asks). The top row shows the best bid and best ask, together forming the current bid-ask spread. The deeper levels show additional price points and the aggregate depth or the size of available liquidity at those prices. The order book is central to price discovery and liquidity provision, as it reveals supply and demand at different prices and how much can be traded at each level.

Orders enter the book as limit orders or cancel existing ones as market orders are executed. Market orders consume liquidity by matching with the best available limit orders; limit orders add liquidity and improve depth. Matching engines use price-time priority: higher-priced bids win against lower ones; earlier orders of equal price have priority. Data feeds labeled Level I show best bid and ask, while Level II or depth feeds disclose deeper levels of the book; access varies by venue and subscription.

Not all orders are visible; some venues use dark pools or hidden orders. Traders use order book information for strategies such as liquidity provisioning, detecting imbalances, or timing trades. The term order book is used in many markets, and the exact rules (tick sizes, lot sizes, and cancellation policies) depend on the exchange.