Trading and Exchanges Chapter 5: How Different Market Structures Work (Part 1)
Chapter 5 is where Harris gets into the actual plumbing. You know how in previous chapters we talked about types of traders and types of orders? Now we are looking at the arena where all that happens. Market structure. The rules, the systems, and the “who gets to trade with whom” part.
And honestly, this is one of those chapters where you realize most people have zero clue how their trades actually get processed.
Why Market Structure Even Matters
Market structure is basically the rulebook of a market. It decides who can trade, what they can trade, when and how they can trade, and what information everyone gets to see.
Why should you care? Because the structure determines who has power. Knowledge plus ability to act on it equals power. Different market structures create different power dynamics among traders. The strategy that makes you money on one exchange might bleed you dry on another, simply because the rules are different.
Harris puts it simply: you cannot understand liquidity, price efficiency, or volatility without understanding market structure first.
Continuous Markets vs Call Markets
There are two fundamental types of trading sessions. Continuous and call.
Continuous markets are what you’re used to. The market is open, you can trade anytime during trading hours. NYSE opens at 9:30 AM, closes at 4 PM Eastern. During that window, you submit orders whenever you want. Most major stock, bond, futures, and forex markets work this way.
Call markets are different. Everyone trades at the same time when the market is “called.” Think of it like an auction where all bids come in, and then bang, everything gets matched at once. Governments sell their bonds this way. Some European exchanges use calls for their least active stocks.
Here is a fun analogy from the book. Horse racing betting is a call market. In pari-mutuel betting, everyone places bets until the race starts, then the totalizator system calculates all the payoffs at once. That is literally a call market auction. Smart bettors wait until the last second to place bets so they can see what the odds look like. Same principle as watching a call auction build up.
The tradeoff is straightforward. Call markets are great at focusing all buyers and sellers at the same moment, which helps everyone find each other. Continuous markets let impatient traders trade whenever they want without waiting for the next call.
Interestingly, most continuous exchanges now open with a call auction and then switch to continuous trading. Nobody has gone the other direction, from continuous back to calls-only. Traders clearly prefer the flexibility.
One cool detail: in continuous markets, traders can “ping” the market by submitting orders just to see what happens. It is like sonar for prices. You throw something in and listen for the echo.
The Three Execution Systems
Now here is the core of this chapter. Every market has a system for matching buyers with sellers. Harris identifies three main types.
Quote-Driven (Dealer) Markets
In a pure dealer market, every trade goes through a dealer. You want to buy? You buy from a dealer. You want to sell? You sell to a dealer. Regular people cannot trade directly with each other.
Think of it like a used car lot. You cannot just sell your car to the next buyer who walks in. You sell to the lot, and the lot sells to the buyer. The dealer makes money on the spread between buy and sell prices.
Harris has a great example with sports bookies. A bookie is literally a dealer in a quote-driven market. They quote odds on both sides, try to keep their book balanced, and profit from the vigorish (the spread). A typical football bet has about a 10% vig. When their book gets lopsided, bookies “lay off” risk by placing bets with other bookies, paying the vig to do so. And ruthless bookies, well, they have their own credit risk management techniques involving kneecaps.
Most bond and currency markets are dealer markets. The old Nasdaq was a classic dealer market too, though it evolved over time. Dealers choose who they want to trade with. They avoid well-informed traders (because informed traders tend to win), they prefer certain clienteles, and they use interdealer brokers to trade anonymously among themselves.
Order-Driven Markets
In order-driven markets, buyers and sellers trade directly with each other. The market has rules that match orders automatically. No dealer middleman required (though dealers can still participate if they want).
These are auction markets. The rules formalize how buyers seek the lowest prices and sellers seek the highest. Economists call this price discovery.
Order-driven markets come in several flavors. Single-price auctions match everything at one price after a call. Continuous two-sided auctions let traders constantly try to match at prices that move through time. Crossing networks match orders at prices taken from other markets.
eBay is actually a perfect example. It runs millions of pure order-driven auctions simultaneously. Each listing is a call market where buyers submit limit orders and the highest bidder wins. The “buy it now” feature is basically someone taking a standing offer before the auction closes.
The biggest difference from dealer markets: in order-driven markets, you cannot choose your counterparty. The rules decide who trades with whom. This creates credit risk, which is why these markets have elaborate systems to make sure everyone can actually pay up.
Brokered Markets
Brokered markets exist where things are too unique or too large for regular markets. Brokers actively search for buyers and sellers instead of waiting for orders to come in.
Think real estate. There is no order book for houses. A broker has to go find someone who actually wants to buy that specific property. Same idea applies to large blocks of stocks or bonds. A regular exchange can handle 1000 shares no problem, but if you need to move 5 million shares, you need a broker to quietly find someone on the other side.
Brokers deal with two interesting types of traders. Concealed traders who want to trade but will not show their hand publicly. And latent traders who do not even know they want to trade until a broker shows them a good enough deal.
Hybrid Markets
In reality, most big markets are hybrids. The NYSE is mainly order-driven but requires specialist dealers to provide liquidity when nobody else will. The old Nasdaq was mainly dealer-driven but required dealers to display public limit orders. Both had brokers handling large block trades. Clean categories are for textbooks. Real markets mix and match.
Market Information Systems
The last section of Part 1 covers how information flows. Markets produce data about trades, quotes, and orders. This data is extremely valuable. Who gets to see what, and when, has a huge effect on who profits.
Electronic markets have a natural advantage here because all information is already digital. Floor-based markets have to employ human reporters sitting on podiums above trading pits, using hand signals and wireless devices to report what is happening. Expensive and slow.
Data vendors like Bloomberg and Reuters reformat raw market data into something usable. Traders pay for real-time feeds. Everyone else gets delayed data, 15 or 20 minutes behind. Exchanges charge separate fees for real-time access because they know the people who need it will pay.
Toronto Stock Exchange members, for example, could see the full limit order book. Public traders only got aggregate sizes at the best five prices on each side. Information asymmetry baked right into the system.
In Part 2, we will cover order precedence rules, trade pricing rules, and how the order book actually works.
Previous: Chapter 4: Orders and Order Properties