What Is an ETF? How They Actually Work

An ETF is a fund you can buy and sell during the trading day, the same way you buy a share of a company. That is the short answer, and it is the one you will find everywhere.

The longer answer is more useful, because the thing that makes an ETF work is a mechanism most explanations skip entirely. Once you understand it, a lot of other questions stop being separate questions.

I run an ETF business, so what follows is how it works from the inside.

What you are actually buying

An ETF holds a basket. It might be five hundred stocks, or ten bonds, or a mix of both. Buy one share of the fund and you own a proportional slice of everything in it.

That part is identical to a mutual fund. A mutual fund also holds a basket and also gives you a slice of it.

The difference is when and how you buy.

A mutual fund prices once a day. After the market closes, the fund adds up what its holdings are worth, divides by the shares outstanding, and that is the price everybody gets. Orders placed at eleven in the morning and at three in the afternoon settle at the same number.

An ETF trades all day on an exchange. There is a price at 9:31 and a different one at 2:14, set by whoever is buying and selling at that moment.

That difference sounds like a convenience, and it creates a problem.

ETF, index fund, mutual fund

These three get used interchangeably and they are answers to different questions.

Mutual fund describes the legal wrapper and how you transact. You buy from the fund company, once a day, at the closing value.

ETF also describes a wrapper and how you transact. You buy from another investor on an exchange, any time the market is open.

Index fund describes the strategy, not the wrapper. It means the fund follows a published index instead of a manager picking holdings. An index fund can be a mutual fund or an ETF. Plenty of ETFs are not index funds at all, because they are actively managed.

So "index fund versus ETF" is not really a choice between two things. The real questions are whether you want indexed or active, and whether you want to trade intraday or once a day. Those are independent.

The question nobody answers

If buyers and sellers set the price, what stops it from drifting away from what the fund actually holds?

A fund holding a hundred dollars of stock should trade around a hundred dollars. Nothing about an exchange forces that. Traders set the price, and traders can be wrong, or panicked, or simply absent.

This is the question most explanations walk past. It is also the one that matters, because the answer explains almost everything else an ETF does.

Authorized participants

Every ETF has a small group of large trading firms attached to it. They are called authorized participants, and they hold a privilege nobody else has: they can go to the fund and create brand new shares, or hand shares back and have them destroyed.

Ordinary investors cannot do this. As Brett Eichenberger put it on Behind the Ticker while explaining how ETF audits work, these transactions are "with authorized participants, not individual shareholders".

That one privilege is what keeps the price honest.

The trade that closes the gap

Suppose the fund holds a hundred dollars of stock per share, but the shares are changing hands at a hundred and one.

An authorized participant buys the underlying stocks in the market for a hundred. It delivers those stocks to the fund. The fund issues it new ETF shares in exchange. It sells those new shares into the market at a hundred and one.

It keeps a dollar. And because it just created new shares, supply went up and the price drifted back toward a hundred.

Now suppose the shares are trading at ninety nine, below what the fund holds. The trade runs in reverse. The participant buys the cheap shares in the market, hands them to the fund, receives the underlying stocks, and sells those. It keeps the difference again, and by removing shares from the market it pushes the price back up toward fair value.

Nobody is doing this out of goodwill. There is a dollar in it. That profit motive is what keeps the price near the value of the holdings, all day, every day, without anyone supervising it.

David LaValle of Grayscale described this as "the hallmark and kind of the bedrock of how an ETF" functions, and he is right. Almost everything else follows from it.

Who is actually on the other side

Sitting alongside the authorized participants are market makers, who quote continuous buy and sell prices so there is always someone to trade with.

Paul Weisbruch of GTS gave a sense of the scale on the show, describing his desk quoting bid and ask prices for "340 some odd names right now" simultaneously.

Sean O’Hara of Pacer made the point that this depends on real capital. The industry, he said, "really relies upon the market makers and in particular their balance sheet".

Worth remembering when a fund looks quiet. There is usually infrastructure behind it that is not visible in the volume number.

Three things that follow

Once the mechanism is clear, three commonly cited ETF features stop looking like separate facts.

Prices track holdings closely. Not perfectly. The gap widens when the underlying market is thin, volatile, or closed, which is why an ETF holding Japanese stocks can drift during New York hours. But closely, most of the time, because there is money in closing the gap.

Most ETFs are tax efficient. When a large holder exits, the fund can hand over stock instead of selling it. No sale means no realized capital gain, which means nothing is passed through to everyone still in the fund. A mutual fund in the same position often has to sell, and the remaining shareholders receive the tax bill. This comes up constantly with practitioners, and it is structural rather than clever.

Low trading volume does not mean illiquid. This is the most commonly misread number in the category. An ETF’s real liquidity comes from the liquidity of what it holds, because a participant can always create or redeem against the underlying. A fund trading a few thousand shares a day that holds large cap US stocks is far easier to move than the volume figure suggests.

What to check before you buy one

Four things, and none of them are the ticker.

What it holds. ETFs publish their holdings daily. Open the file once. Funds with similar names frequently hold very different things, and the name is marketing while the holdings file is fact.

What it costs. The expense ratio comes out of the fund every year, quietly, without a line on your statement. On the show, fund managers state theirs plainly. Raymond Bridges named his at 0.78% while explaining what it does and does not cover. Ask what you get for it.

The spread. The gap between the buy and the sell price is a real cost, paid on the way in and again on the way out. On a widely traded fund it is negligible. On a thin or exotic one it is not, and it can quietly exceed a year of expenses.

Whether it does what the name says. A fund called low volatility might select genuinely low volatility stocks, or it might select sectors that happened to be calm recently. Those behave very differently when conditions change. The name will never tell you which one you own.

The part worth keeping

An ETF is a basket you can trade like a stock, held near fair value by a group of firms with a financial reason to keep it there.

The wrapper is simple, well tested, and mostly does what it claims. What matters is what somebody put inside it, what they charge you for it, and whether it behaves the way the label implies.

Those are questions about the fund. The wrapper is just a wrapper.

This is educational content and not investment advice. It is not a recommendation regarding any security. Investing involves risk, including possible loss of principal. Past performance does not guarantee future results.