What Is a Stock Exchange? How It Works, and Where US Stocks Really Trade (2026)
Michael Whitman
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Trading since 2017, full-time since 2020
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YouTube creator, 137K subscribers
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Published 2026-09-06
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Updated
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Reviewed
A stock exchange is a regulated venue that matches buy and sell orders under published rules. It sets listing standards for the companies traded on it, runs the opening and closing auctions, and publishes the prices and trades its own matching produces.
A stock exchange is a regulated marketplace that does two things: it decides which companies may list their shares there, and it runs the computer that matches buyers with sellers under rules registered with the Securities and Exchange Commission. The NYSE and Nasdaq are the two names most people know.
What most explanations leave out is how much of the US market sits outside them. In September 2026, by Cboe’s daily figures, slightly more than half of all shares, and 47.75% of the dollars, changed hands away from any exchange.
How it works
In simple words: an exchange is a queue with a rulebook. Every buy order waits at its price, every sell order waits at its price, and a trade happens when the two meet. Strip away the trading floor and the history, and what remains is software applying a published priority rule.
The priority rule is price, then time. A higher bid goes ahead of a lower one and a lower offer ahead of a higher one. Among orders at the same price, the earliest is filled first. The order book is that queue as a trader sees it on screen.
Opening and closing are auctions, not ordinary trades. The core US session runs from 9:30 a.m. to 4:00 p.m. Eastern time (NYSE hours page, read 1 November 2026). Before the open and at the close, the listing exchange collects orders and strikes one price that lets the most shares trade. Those two prints become the official open and close, which is why index funds crowd into the closing auction: they must trade at the official close.
The opening price is a clearing price, not the start of a trend. It settles the overnight imbalance in one print, and it can sit well away from the previous close with no continuous trading in between.
What it takes to list, and to stay listed
Listing is the second job. An exchange publishes minimum standards, such as share price, market value, number of holders, governance and reporting, and companies that meet them may list. The exchange then keeps checking. A company that falls below a continued-listing standard is flagged and given time to fix it before delisting.
The flags are public. Nasdaq’s daily symbol file marks each listing’s financial status. On 27 October 2026, 343 of Nasdaq’s 4,327 non-ETF listings (7.93%) carried a flag: 322 deficient (failing a continued listing requirement), 15 delinquent (a missed filing deadline) and 6 both.
The flag rate rises as the entry bar falls: 16 of 1,440 (1.11%) on the Global Select Market, 68 of 1,214 (5.60%) on the Global Market and 259 of 1,673 (15.48%) on the Capital Market.
Registration is the price of operating. Section 5 of the Securities Exchange Act of 1934 (15 U.S.C. 78e, read on govinfo.gov on 3 October 2026) bars brokers and dealers from using an exchange that is not registered as a national securities exchange, unless the SEC has exempted it for low volume.
Section 6 sets the bar. Under section 6 (15 U.S.C. 78f), an exchange files its rules with the SEC, which registers it only if it can comply with the securities laws and enforce its members’ compliance. Every later rule change is filed and posted for comment.
A worked example: one day, two kinds of venue
Take Wednesday 30 September 2026, the last session of the quarter. Cboe’s market-volume page for that day reports 18,724,868,643 shares traded across all US venues.
- On exchanges: 9,356,034,346 shares, 49.97% of the total.
- Off exchange, reported to FINRA’s trade reporting facilities: 9,368,834,297 shares, 50.03%.
- In exchange auctions: 1,750,913,123 shares, 9.35% of the day, found by subtracting Cboe’s auction-excluded exchange total (7,605,121,223) from the full one.
Read it as a split down the middle. Roughly one share in two never reached an exchange’s book that day, and close to one share in ten changed hands at a single auction price. Those off-exchange trades were not hidden for long: FINRA Rule 6380A (read 3 October 2026) requires a firm reporting to the FINRA/Nasdaq trade reporting facility to send each trade “as soon as practicable but no later than 10 seconds after execution”.
The original data
Who lists what. Nasdaq Trader publishes two symbol directory files a day, one for Nasdaq listings and one for every other US exchange, each with the listing exchange, an ETF flag and a test-issue flag. The files created at 3:03 a.m. Eastern on 27 October 2026 hold 13,289 rows; 37 test symbols are left out.
| listing exchange | securities listed | ETFs | everything else |
|---|---|---|---|
| Nasdaq | 5,611 | 1,284 | 4,327 |
| NYSE | 2,886 | 79 | 2,807 |
| NYSE Arca | 2,746 | 2,729 | 17 |
| Cboe BZX | 1,677 | 1,673 | 4 |
| NYSE American | 310 | 0 | 310 |
| Texas Stock Exchange | 22 | 10 | 12 |
Two of the six listing exchanges are fund venues. 99.38% of what NYSE Arca lists and 99.76% of what Cboe BZX lists are ETFs, and between them they list 76.23% of the 5,775 ETFs in the files. Operating companies, ADRs, preferred shares, warrants and units sit mostly on Nasdaq and the NYSE.
The check: the SEC’s own ticker file puts 6,934 of the 6,937 non-ETF symbols found in both files on the same exchange family; the other 3 have no exchange in the SEC file. The rows are in the listings file and the Nasdaq status file.
Who trades it. Cboe’s US equities pages, read on 3 October 2026, give each venue’s share of shares traded for every session of each September from 2021 to 2026, auctions included. In September 2026 an average of 16.99 billion shares traded a day over 21 sessions:
| venue group | share of shares traded |
|---|---|
| off exchange (FINRA trade reporting facilities) | 50.63% |
| NYSE’s five exchanges | 19.80% |
| Nasdaq’s three exchanges | 14.38% |
| Cboe’s four exchanges | 8.55% |
| Investors Exchange (IEX) | 4.19% |
| MEMX | 1.64% |
| MIAX Pearl | 0.61% |
| Texas Stock Exchange | 0.15% |
| 24X National Exchange | 0.04% |
| Long-Term Stock Exchange | 0.01% |
Counted in dollars, the move away from exchanges is steeper. The same Cboe figures give the off-exchange share of the dollar value traded. It was 35.30% in September 2021 and 47.75% in September 2026, a rise of 12.45 percentage points, while the share counted in shares rose 8.71 points, from 41.92% to 50.63%. September by September from 2021, the dollar share read 35.30%, 39.01%, 42.34%, 44.55%, 44.11% and 47.75%, and the share of shares 41.92%, 41.66%, 44.13%, 47.47%, 50.97% and 50.63%.
The share count always runs above the dollar share. In every September from 2021 to 2026 the off-exchange share of shares was higher than its share of dollars, by between 1.79 points (2023) and 6.86 points (2025); it was 6.62 points in 2021 and 2.88 in 2026. A share-count share above the dollar share means the off-exchange trades were, on average, in lower-priced shares. The gap jumps around from year to year, so these six monthly totals do not show a trend in which stocks trade away from exchanges.
The yearly figures are in the venue share file, and the daily September and October figures in the off-exchange daily file.
Exchange, stock market, or something else?
The stock market is the whole system; an exchange is one venue in it. A Nasdaq-listed share trades on all 18 exchanges at once and off exchange as well, and the best bid and offer shown on a quote screen is assembled from every exchange’s quotes.
Off-exchange venues come in two kinds. Dark pools run as alternative trading systems that match orders without showing them first. Wholesalers fill retail orders against their own inventory, often paid for through payment for order flow. Both report their trades through FINRA’s facilities.
Over-the-counter stocks are different again. Those are shares not listed on any exchange, quoted by dealers instead, and they do not meet an exchange’s listing standards in the first place.
And an exchange never holds your shares. Your broker does, and the ownership record sits with a central depository; the transfer after each trade is settlement.
When it fails
A fair queue can still give a poor fill. A market order sent into a thin book takes whatever resting orders are there, at their prices. The matching engine did its job; the trader did not check the book.
Auctions can strike odd prices. An opening auction on light interest can print far from where the stock trades ten minutes later, and every order left in it gets that print.
Trading can stop entirely. News halts, single-stock volatility limits and market-wide circuit breakers all suspend matching, and during a halt nothing fills, including a protective stop.
A listing is not due diligence. A company can meet every standard on the day it lists and slip below them later, as the Capital Market flag rate above shows.
Questions people ask
What is a stock exchange in simple words?
A regulated marketplace where listed shares are bought and sold. It matches buy and sell orders by price and time, and it decides which companies may list there.
How does a stock exchange work?
Buyers and sellers send orders through brokers; the exchange queues them by price and arrival time and executes a trade when a bid meets an offer. Auctions set the official open and close.
Which is the largest US stock exchange?
By number of listings, Nasdaq: 5,611 on 27 October 2026, against 2,886 on the NYSE. By share of trading, NYSE’s five exchanges together handled 19.80% of shares in September 2026 and Nasdaq’s three 14.38%.
Do most stock trades happen on an exchange?
Not in September 2026: exchanges handled 49.37% of shares traded, and 50.63% traded off exchange and was reported to FINRA.
Related
The order book is the queue an exchange operates. Trading sessions sets out the hours and why they matter. And market makers keep quotes on both sides of that queue through the day.
I size differently around the open and the close, because both are auctions rather than continuous trading. They are the two moments the whole market agrees to meet at once, and treating them as just more bars is how you end up with a fill you did not expect.
— Michael Whitman
This page is educational, not financial advice. Test every idea on your own charts before risking money.