Exchange Traded Funds (ETFs) are a group of passive index funds that trade on an exchange like an individual stock. At the time of writing there are 162 ETFs with $220 billion in assets under management trading on U.S. exchanges.

ETFs hold a basket of securities that mimic the results of various indices including broad stock and bond market, industry sectors, and international securities. New niche funds are being created regularly. Recent introductions include gold and China funds, and there are rumors that a silver ETF will soon be available.

The most popular ETF is the NASDAQ 100 Tracking Stock (QQQQ) trading 50 million shares a day on the NASDAQ Stock Market. The volume leaders on the American Stock Exchange are the SPDRS (SPY) tracking the S&P 500 trading 25 million shares per day, the Energy SPDR (XLE), Japan iShares (EWJ), Russell 2000 iShares (IWM), and the Financial SPDR (XLF).

ETFs are widely used by institutional and individual investors as a tool for diversification, risk reduction, hedging, and an efficient way to acquire a basket of securities providing partial ownership in all holdings with only a single commission and small administration fees. ETFs are also transparent, meaning that investors know at all times what securities they are invested in.

There are now also options and futures contracts trading on of ETFs. The Chicago Board Options Exchange (CBOE) lists 43 options on ETFs, while the Chicago Mercantile Exchange (CME) offers futures contracts on the S&P 500 Depository Receipts, NASDAQ 100 Tracking Stock, and Russell 2000 Index Fund. And One Chicago, a joint venture between the CBOE, CME, and Chicago Board of Trade (CBOT), offers an electronically traded futures contract on the DIAMONDS Dow Jones Industrial Average ETF.

There are also a number of web sites offering information on Exchange Traded Funds. Check out Amex.com, Yahoo! Finance’s ETF Center, ETFConnect, or ETFera.com. Meanwhile, investment research firm Morningstar compares the fair value estimates to market prices of exchange traded funds holdings to determine whether a fund is over or undervalued.

Exchange Traded Fund’s low costs, liquidity, and diversification make them an excellent alternative to mutual funds, broad based index investments, and individual stocks in niche sectors.