The simple version

An exchange-traded fund, or ETF, is a basket of investments you can buy and sell on an exchange like a single stock. The part most people never see is that the number of ETF shares is not fixed. It can grow and shrink.

That happens through a process called creation and redemption, run by large institutions. It sounds like plumbing, and it is, but it is the reason an ETF's price usually stays near the value of its portfolio instead of wandering away from it.

The numbers

• Retail investors can buy and sell ETF shares only in market transactions; the ETF itself does not sell shares to or redeem shares from them directly (U.S. Securities and Exchange Commission, Investor.gov; Financial Industry Regulatory Authority, FINRA)
• ETFs contract with financial institutions called authorized participants, which typically are large broker-dealers (U.S. Securities and Exchange Commission, Investor.gov; Financial Industry Regulatory Authority, FINRA)
• Authorized participants buy and redeem shares directly with the ETF only in large blocks called creation units, for example 50,000 ETF shares (U.S. Securities and Exchange Commission, Investor.gov)
• To create shares, an authorized participant deposits a designated basket of securities and cash with the ETF and receives ETF shares, which it is free to sell on an exchange to retail investors, institutions, or market makers (U.S. Securities and Exchange Commission, Investor.gov)
• Redemption is the reverse: the authorized participant buys a large block of ETF shares on the open market, delivers them to the fund, and receives a pre-defined basket of securities or the cash equivalent (U.S. Securities and Exchange Commission, Investor.gov)
• The exchange is typically in-kind, a basket of securities and other assets that generally mirrors the ETF's portfolio (U.S. Securities and Exchange Commission, Investor.gov)
• An ETF's market price is typically somewhat above or below its net asset value, or NAV, per share, and is generally kept close to its end-of-day NAV by the arbitrage built into the structure (U.S. Securities and Exchange Commission, Investor.gov)

How trading baskets keeps the price honest

Start with the problem it solves. An ETF has two prices at once: the price its shares trade at on the exchange, and the value of the investments inside it, its NAV. Nothing automatically forces those two to match. The market price moves through the day with supply and demand, so it can sit at a premium or a discount to the value underneath.

Creation and redemption is the force that pulls them together. If demand pushes the ETF's market price above the value of its portfolio, one of these big institutions can assemble the underlying basket, trade it to the fund for new ETF shares at NAV, and sell those shares on the exchange for a small profit. That adds supply and nudges the price back down.

It works in reverse too. If the ETF trades below the value of its portfolio, the institution buys the underpriced ETF shares, returns them to the fund, and takes the basket of securities, which is worth more, again pocketing the gap. That removes shares and pushes the price back up. The profit motive does the work, and the expected result, in the SEC's words, is that the market price moves back in line with NAV.

One more thing falls out of this. Because the trades are usually in-kind, the fund usually meets a redemption by handing over securities rather than selling them for cash. Whether that matters for your taxes is a separate question for a tax professional.

What this means

For an everyday investor who just buys an ETF in an app, none of this is visible, but it is why the ETF you bought trades close to the value of what it holds instead of floating off on its own. The creation and redemption machinery, run by institutions chasing small arbitrage profits, is doing that work in the background.

The durable point is that an ETF is not just a basket you buy; it is a basket with a pressure valve. That valve, the ability to create and redeem shares at the value of the holdings, is the structural feature that keeps its price honest.

What this is NOT

This is not advice to buy, sell, or hold any ETF, fund, or security, and it is not a recommendation of exchange-traded funds over any other kind of fund. It explains how ETF shares are created and redeemed, as the U.S. Securities and Exchange Commission and the Financial Industry Regulatory Authority describe the process; the point about arbitrage keeping the price close to NAV comes from the SEC bulletin alone. It does not cover the tax treatment of ETFs or mutual funds, which is a separate question for a tax professional. It is not a claim that an ETF's price always equals the value of its holdings; the mechanism keeps them close, not identical. This is not a political endorsement or criticism of anyone.

Sources

• U.S. Securities and Exchange Commission, Investor.gov, Investor Bulletin: Exchange-Traded Funds (ETFs), read November 12, 2026: https://www.investor.gov/news-alerts/investor-bulletins/investor-bulletin-exchange-traded-funds-etfs
• Financial Industry Regulatory Authority, Exchange-Traded Funds and Products, read November 12, 2026: https://www.finra.org/investors/investing/investment-products/exchange-traded-funds-and-products