An order book is the central registry of all open buy and sell orders for an asset on a trading platform. It shows the prices at which market participants are willing to buy or sell, forming the basis for price discovery, liquidity, and efficient trading.
The order book continuously lists active limit buy and sell orders, sorted by price and quantity. It makes market interest visible, indicates liquidity, and enables traders to find the best available price. As such, the order book is considered a core instrument for transparently matching supply and demand.
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How an order book works
An order book divides open orders into two sides: the buy side (bids) and the sell side (asks). Each order contains a price and the desired quantity. When matching orders meet, a trade occurs. The price at which the last transaction happens is displayed as the market price.
Order books are updated in real time and show not only current orders but also the so-called “market depth” – the amount of volume available at different price levels. The deeper the market, the more stable the price, as larger trades can be absorbed without causing sharp price swings.
Order books in the Web3 context
While centralized exchanges traditionally manage order books on servers, decentralized trading venues increasingly move this model on-chain or use hybrid systems. An order-book DEX uses the same structure as traditional markets, supplemented by self-custodied assets and often off-chain matching to improve efficiency.
Platforms such as dYdX or Injective bring this mechanism into the crypto sector and enable professional trading strategies like limit orders, stop orders, and derivatives trading in a decentralized environment.
