ETFs: How They Work

That second half is the interesting part and the reason ETFs get their own article rather than a paragraph. A mutual fund creates and cancels units directly with each investor at NAV; an ETF does not. Instead it deals only with a small number of large financial institutions, in large blocks, and everyone else buys and sells existing units from other investors on the exchange. The arrangement sounds like it should produce a price that drifts away from the portfolio's value — and the mechanism that stops it, creation and redemption, is genuinely the most elegant piece of plumbing in retail finance. This article explains it, then explains what it means for the reader in practice.

Two markets, and the mechanism that links them

An ETF operates in two distinct markets simultaneously, and keeping them separate is the key to understanding everything else. The secondary market is where you transact: units trade on an exchange, at a market price set by supply and demand, continuously through the session, with a bid-offer spread and all the ordinary venue mechanics. Your counterparty is another investor or a market maker; the fund is not involved and its size does not change. The primary market is wholesale. A small set of institutions designated as authorised participants (APs) have the contractual right to deal directly with the fund, but only in large blocks called creation units — typically tens of thousands of ETF shares at a time. An AP can deliver the underlying basket of securities to the fund and receive new ETF shares in exchange (creation), or deliver ETF shares back and receive the underlying securities (redemption). Critically, this exchange is normally in kind — securities for shares, not cash — which is the feature that produces several of the ETF's distinctive properties. Now the link, which is arbitrage. Suppose demand pushes an ETF's market price above the value of its underlying holdings. An AP can buy the underlying basket, deliver it to the fund, receive new ETF shares, and sell them on the exchange at the higher price, pocketing the difference — and in doing so it has increased the supply of ETF shares, which pushes the price back down toward the portfolio's value. If the price falls below the underlying value, the reverse: buy cheap ETF shares on the exchange, deliver them to the fund, receive the more valuable basket, sell it. That reduces supply and pushes the price up. The profit motive of the APs is what keeps an ETF's price tethered to its portfolio, and it operates continuously, without the fund needing to do anything. Note what makes it work: the arbitrage must be cheap and reliable, which requires the underlying securities to be tradeable at known prices. Where they are not — thinly traded bonds, closed foreign markets, unusual assets — the tether stretches, which is why premiums and discounts are larger in some ETFs than others and why ETF liquidity needs its own article.

What the mechanism produces

Five consequences, and they explain most of what people notice about ETFs. Intraday dealing at a known price. Unlike a mutual fund's forward pricing, you see the price before you commit and can use limit orders — a real practical difference, and one that cuts both ways, since the ability to trade continuously is also the ability to trade impulsively. Transparency of holdings. Because APs need to know the basket to arbitrage it, most ETFs publish holdings daily, which is far more disclosure than a typical mutual fund provides. Related: providers publish an indicative NAV (iNAV) through the session — an estimated live value of the portfolio, useful for judging whether the current market price is near fair value, and itself only an estimate. Insulation from other investors' trading. This is underappreciated and matters. When another investor sells an ETF, they sell to a buyer on the exchange; the fund does not sell securities, so the fund incurs no dealing cost — which means the flow-cost externality that afflicts open-ended funds is largely absent. Transaction costs sit with the transacting investor, in their spread and commission, rather than being socialised across all holders. Tax-efficiency mechanics. Because redemptions are met by delivering securities in kind rather than by selling them, the fund can often avoid realising gains it would otherwise realise — a structural feature with consequences that vary enormously by jurisdiction, holder, and wrapper. This portal states that the mechanism exists and does what it does; the tax outcomes are parked to Annex A and belong with a qualified adviser, because they are among the most jurisdiction-specific matters in this pillar. And costs are typically lower, for reasons partly structural — no need to service individual investor accounts, no cash buffer required for redemptions — and partly competitive. Two honest qualifications. The in-kind mechanism is not universal: some ETFs, particularly in certain asset classes and jurisdictions, use cash creation and redemption, which changes the tax and cost properties. And the arbitrage mechanism depends on APs choosing to participate; in extreme stress, APs have stepped back, and the tether has stretched — a documented phenomenon in specific episodes rather than a routine occurrence, but a real limit on a mechanism sometimes described as automatic.