What it is

A market price is not handed down from above - it is the running result of orders meeting orders. To understand why price moves, you have to know who is sending those orders and how the marketplace matches them.

Market structure is the set of rules and venues through which orders are routed, matched, and reported. Participants are the different kinds of traders pushing orders into that structure. Their combined behaviour - their order flow - is what actually moves price.

How it works

The participants fall into a few broad groups.

• Retail traders: individuals trading their own accounts through a broker. Each order is usually small, but collectively retail flow is large and can cluster around the same popular names.
• Institutional traders: funds, pensions, and asset managers handling huge sums. A single institutional decision can mean millions of shares, so they often break orders into pieces to avoid moving the market against themselves.
• Market makers: firms that continuously quote both a bid price and an ask price, standing ready to buy and sell. They provide liquidity and earn the bid-ask spread as compensation for the risk of holding inventory.

A market maker's job is to be the always-available counterparty. When you hit the market with a market order, a market maker is frequently on the other side. They profit by buying at the bid and selling at the ask many times over, not by predicting direction. Because they hold inventory between trades, they widen their quoted spread when risk rises - thin liquidity, pending news, or wild volatility all push the spread out to compensate them.

Beyond these three, other players matter at the margin: high-frequency trading firms that arbitrage tiny price gaps in microseconds, hedge funds running directional bets, and corporate buyers repurchasing their own shares. Each adds order flow with its own motive, but the same mechanics apply to all of them - every order either adds liquidity (a resting limit order) or removes it (a marketable order that consumes the book).

Why flow moves price

Price moves because liquidity at each level is finite. Picture the order book as a stack of resting orders at different prices.

1. A wave of buy orders consumes the shares offered at the best ask.
2. Once that level is exhausted, the next buyer must pay the next-higher ask to get filled.
3. The best ask ratchets up, and the quoted price rises.

The reverse happens with heavy selling. So a large institutional buyer who must accumulate a position will, by consuming offers, push price up as they go - which is exactly why they slice orders to hide their footprint. Imbalance between buying and selling pressure, not any single 'correct' value, is what nudges price tick by tick.

How to use it

Use this lens to read what is happening behind a price move:

1. Ask who is likely trading. A sharp move on heavy volume hints at institutional flow; a frenzy in a small, popular stock often smells of clustered retail activity.
2. Watch volume with price. A move backed by rising volume reflects real flow; a move on thin volume can reverse easily.
3. Respect the market maker's spread. In illiquid names the spread is the market maker's premium for standing in - and your cost for demanding immediacy.
4. Think in terms of imbalance. Ask whether buyers or sellers are the aggressors consuming resting liquidity, rather than searching for a single fair price.

A short pre-trade checklist keeps these habits sharp:

• Is volume unusually high or low relative to the stock's normal day?
• Is the spread tight (liquid, easy to exit) or wide (thin, costly)?
• Does the price move have follow-through, or does it stall as soon as the aggressive flow pauses?
• Could a single large participant plausibly explain what I am seeing?

A worked example

Suppose a fund decides to buy 500,000 shares of a mid-size company that normally trades 200,000 shares a day. If it sent one giant market order, it would blow through every resting offer and spike the price against itself. Instead it works the order over days, buying in small clips, often near the bid to let liquidity refill. A market maker quotes against each clip, pocketing the spread. Retail traders, seeing steady buying and a slowly rising price, may pile in - adding flow that pushes price further. The visible result is a gentle uptrend; the hidden cause is one large participant managing its footprint through the market's structure.

Key takeaway: Price is the live scoreboard of order flow - knowing whether retail or institutional pressure dominates, and how market makers bridge the two, explains the moves you see.

Strengths & limits

Reading markets through participants and flow is powerful because it ties price to real behaviour rather than abstract value. It explains why news can move price little (already positioned for) or hugely (caught the crowd offside). The limits matter too. As an outsider you rarely see who is trading in real time - you infer it from volume, spread, and price action, and those inferences can be wrong. Flow can also be deliberately disguised through tactics like iceberg orders that hide their true size, and a market maker's quotes reflect inventory risk, not a forecast. The same price print can have entirely different meanings depending on who was behind it, and you will rarely know for certain. Treat the participant lens as a strong interpretive framework that sharpens your reading of volume and price, not a precise, observable readout you can take literally.