Market Microstructure: Order Books & Execution Mechanics › Market Microstructure and Order Types

When you submit an order to buy 1,000 shares of Apple, what happens? The answer is far more complex than "someone sells it to you." Your order enters a network of competing exchanges, order books, matching engines, and execution protocols that determine whether your trade executes, at what price, in what sequence, and with what impact on subsequent prices.

Market microstructure is the study of how trades are executed and prices are formed at the granular level. While traditional finance often treats markets as frictionless, assuming you can buy or sell any quantity at the current price, reality is messier. Orders queue in electronic order books, compete for execution priority, and leave footprints that move prices. Understanding these mechanics is essential for you to translate theoretical strategies into actual executed positions.

Building on our discussion of transaction costs and market impact in the previous chapter, we now examine the underlying plumbing: the order book architecture that determines execution, the taxonomy of order types available to traders, and the rules that govern how orders interact. This knowledge directly informs the execution algorithms we'll develop in the next chapter on optimal execution.