The Bogleheads' Guide to Investing

Exchange-traded funds (ETFs) are basically mutual funds that trade like stocks on an exchange. They are bought and sold continuously throughout the day when the stock market is open. The ETF’s stocklike features appeal to a wide range of investors, including long-term buy-and-hold investors, as well as short-term traders. Perhaps one of the biggest benefits of owning ETFs is the low cost. ETF expenses can be as low, or even lower, than many mutual funds that track the same index.