What Is an ETF?
An ETF (exchange-traded fund) is an investment fund that holds a collection of assets — stocks, bonds, commodities, or other securities — and trades on a stock exchange just like an individual stock. When you buy a share of an ETF, you are buying a small slice of every holding inside the fund.
ETFs have become one of the most popular investment vehicles in the world, holding over $10 trillion in assets globally. Their appeal is simple: they combine the diversification of a mutual fund with the trading flexibility of a stock, usually at a very low cost.
Whether you want exposure to the entire US stock market, a specific sector like technology, or even gold, there is almost certainly an ETF for it. You can browse the full ETF directory to see the range of options available.
How Do ETFs Work?
At its core, an ETF is a basket of securities managed by a fund company (the issuer). The issuer decides what the fund will hold — often by tracking a specific index like the S&P 500 — and handles the day-to-day management.
Unlike mutual funds, which you can only buy or sell at the end of the trading day at a single price, ETFs trade continuously on exchanges like the NYSE or Nasdaq. This means you can buy or sell shares any time the market is open, and the price changes throughout the day based on supply and demand.
Most ETFs are passively managed, meaning they aim to replicate the performance of an index rather than beat it. A fund like SPY simply holds the 500 stocks in the S&P 500 in the same proportions as the index. Some ETFs are actively managed, with portfolio managers making decisions about what to hold.
The Creation and Redemption Process
What makes ETFs structurally unique is the creation and redemption mechanism. This process involves large financial institutions called authorized participants (APs), typically big banks or broker-dealers.
When demand for an ETF rises, an AP assembles a basket of the underlying securities and delivers them to the ETF issuer in exchange for a large block of new ETF shares (called a creation unit, usually 25,000–50,000 shares). The AP then sells those shares on the open market.
When demand falls, the process reverses. The AP buys ETF shares on the market, delivers them to the issuer, and receives the underlying securities back. This is a redemption.
This mechanism serves two critical purposes. First, it keeps the ETF's market price closely aligned with the value of its underlying assets (its net asset value, or NAV). Second, it enables tax efficiency by allowing the fund to remove securities without selling them on the open market.
Types of ETFs
The ETF universe has expanded dramatically. Here are the major categories:
Broad market ETFs track a wide index like the S&P 500 or the total US stock market. Funds like VTI and VOO are among the most popular investments in the world.
Sector ETFs focus on specific industries — technology, healthcare, energy, financials, and more. These let you overweight or underweight specific parts of the economy.
Bond ETFs hold fixed-income securities, ranging from US Treasuries to corporate bonds to international debt. They provide income and can reduce portfolio volatility.
International ETFs provide access to markets outside the US, including developed markets in Europe and Asia and emerging markets like China, India, and Brazil.
Commodity ETFs track the price of physical commodities like gold, silver, or oil. Some hold the physical commodity; others use futures contracts.
Thematic and specialty ETFs target specific trends like artificial intelligence, clean energy, or cryptocurrency. These tend to be narrower and carry higher risk.
Why Choose an ETF Over Other Investments?
ETFs offer several advantages that have made them the default choice for millions of investors:
Low cost. The average ETF expense ratio is significantly lower than the average mutual fund. Many broad-market ETFs charge just 0.03%–0.10% per year. You can compare the cheapest ETFs to find the best deals.
Diversification. A single ETF can hold hundreds or thousands of securities. Buying one share of a total stock market ETF gives you exposure to the entire investable US market.
Tax efficiency. The in-kind creation/redemption process means ETFs rarely distribute taxable capital gains, which can be a significant advantage over mutual funds in taxable accounts.
Transparency. Most ETFs disclose their holdings daily, so you always know exactly what you own. Mutual funds typically disclose holdings only quarterly.
Trading flexibility. You can buy and sell ETFs at any point during the trading day, use limit orders, and even trade options on many popular ETFs.
How to Start Investing in ETFs
Getting started with ETFs requires just a few steps. First, you need a brokerage account — most major brokers like Fidelity, Schwab, and Vanguard offer commission-free ETF trading.
Next, decide what you want to invest in. For beginners, a broad-market ETF like VTI (total US stock market) or VOO (S&P 500) is a strong starting point. You can always add more specialized ETFs later.
Finally, place your order. Use a limit order rather than a market order to control the price you pay. Many brokers now support fractional shares, so you do not need enough money to buy a full share. For a detailed walkthrough, see our guide on how to buy ETFs.
Key Metrics to Understand
When evaluating any ETF, pay attention to these core metrics:
Expense ratio — the annual fee expressed as a percentage. Lower is better for long-term investors.
Assets under management (AUM) — the total value of the fund's assets. Larger funds tend to be more liquid and less likely to close.
Tracking error — how closely the ETF follows its benchmark index. Lower tracking error means more faithful replication.
Trading volume and bid-ask spread — indicators of liquidity. Higher volume and tighter spreads mean lower trading costs.
You can compare all of these metrics side by side using the ETF comparison tool.
Are ETFs Right for You?
ETFs are suitable for virtually every type of investor, from complete beginners to sophisticated institutions. They work for long-term buy-and-hold strategies, retirement portfolios, and tactical trading.
If you want a simple, low-cost, diversified portfolio without picking individual stocks, ETFs are likely the best tool for the job. To learn more about building a complete portfolio, read our guide on how to build an ETF portfolio.
