Why are index funds called index funds?
"Because they track an index. Edited: The definition of the word in this case meaning ""something used or serving to point out; a sign, token, or indication"" from Meaning  #3 I presume therefore you are asking what an index is? There are many variations of what makes up an Index but in short it is a representation of some part of a market. An extremely simplistic calculation would be to take a basket of stocks, and sum their prices.  If one stock moves up a dollar, and one moves down a dollar, the index has effectively not changed, as it is presumed that the loss in one is offset by the gain in the other."
S & P Index Announcements would have notes on when there are changes to the index.  For example in the S & P Small-cap 600 there is a change that takes affect on Feb. 19, 2013. As for how index funds handle changes to the fund, this depends a bit on the nature of the fund as open-end mutual funds would be different than exchange-traded funds.  The open-end fund would have to sell and purchase to keep tracking the index which can be interesting to see how well this is handled to keep the transaction costs down while the ETFs will just unload the shares in the redemption units of the stock leaving the index while taking in new shares with creation units of the newly added stock to the index. "First, consider what causes taxes to apply to a mutual fund, index or actively managed.  Dividends and capital gains are generally what will be distributed to shareholders given the nature of a mutual fund since the fund itself doesn't pay taxes.  For funds held in IRAs or other tax-advantaged accounts, this isn't a concern and thus people may not have this concern for those situations which can account for a lot of investing situations as people may have 401(k)s and IRAs that hold their investments rather than taxable accounts. Second, there can be tax-managed funds so there can be cases where a fund is managed with taxes in mind that is worth noting here as what is referenced is a ""Dummies"" link that is making a generalization.  For taxable accounts, it may make more sense to have a tax-managed fund rather than an index fund though I'd also argue to be careful of asset allocation as to maintain a purity of style can require selling of stocks that grow too big and thus trigger capital gains,e.g. small-cap and mid-cap funds that can't hold onto the winners as they would become mid-cap and large-cap instead of representing the proper asset class. A FUND THAT PLAYED IT SAFE--AND WAS SORRY would be a Businessweek story from 1998 of an actively managed fund that went mostly to cash and missed the rise of the stock market at that time if you want a specific example of what an actively managed fund can do that an index fund often cannot do.  The index fund is to track the index and stay nearly all invested all the time." Index funds are good for diversifying risk. For people who don't have a large sum of money to invest, holding all the different types of stocks in the index is both very expensive and not practical because you incur too many transaction costs. For an index funds, the main advantages are that costs are pooled, and investors can invest a smaller amount that they would if they bought all the different stocks individually. Naturally, if you wanted to figure out the percentage composition of the index and invest directly it would be possible, albeit tedious. "A fund is a portfolio, in that it is a collection, so the term is interchangeable for the most part.  Funds are made up of a combination of equities positions (i.e., stocks, bonds, etc.) plus some amount of un-invested cash. Most of the time, when people are talking about a ""fund"", they are describing what is really an investment strategy.  In other words, an example would be a ""Far East Agressive"" fund (just a made up name for illustration here), which focuses on investment opportunities in the Far East that have a higher level of risk than most other investments, thus they provide better returns for the investors.  The ""portfolio"" part of that is what the stocks are that the fund has purchased and is holding on behalf of its investors.  Other funds focus on municipal bonds or government bonds, and the list goes on. I hope this helps. Good luck!" index ETF tracks indented index (if fund manager spend all money on Premium Pokemon Trading Cards someone must cover resulting losses) Most Index ETF are passively managed. ie a computer algorithm would do automatic trades. The role of fund manager is limited. There are controls adopted by the institution that generally do allow such wide deviations, it would quickly be flagged and reported. Most financial institutions have keyman fraud insurance. fees are not higher that specified in prospectus Most countries have regulation where fees need to be reported and cannot exceed the guideline specified. at least theoretically possible to end with ETF shares that for weeks cannot be sold Yes some ETF's can be illiquid at difficult to sell. Hence its important to invest in ETF that are very liquid. An index fund is inherently diversified across its index -- no one stock will either make or break the results. In that case it's a matter of picking the index(es) you want to put the money into. ETFs do permit smaller initial purchases, which would let you do a reasonable mix of sectors. (That seems to be the one advantage of ETFs over traditional funds...?) Interesting to me.  Index funds are known for hurting active management. Fund flows have been toward index funds, not active funds.  But apparently S&amp;P and MSCI are making hundreds of millions just by licensing out the names of their most popular funds.  Vanguard also had a sweetheart deal at one time:  &gt; Index funds weren't always a big business, and S&amp;P didn't always know just how valuable the indexes it owned really were. Before the first ETF ever hit the market, S&amp;P agreed to a perpetual license with Vanguard that entitled the index owner to a maximum annual fee of $50,000 from Vanguard's premier index mutual fund, the Vanguard 500 Index Fund.  &gt;As Vanguard popularized the index fund, S&amp;P began to realize just how much it had left on the table. By 2001, the Vanguard fund had $90 billion in assets  &gt; To this day, Vanguard's premier S&amp;P 500 index fund is reportedly operating under its perpetual license, paying just $50,000 per year to S&amp;P Global, but subsequent funds based on S&amp;P's indexes are likely paying full freight. For S&amp;P, it was a very costly lesson to learn. "There is no fundamental, good reason, I think; ""that's just how it's done"" (which is what all the other answers seem to be saying, w/o coming out and admitting it). Just guessing, but I'll bet most of the reason is historical: Before up-to-the-moment quotes were readily available, that was a bit tedious to calculate/update the fund's value, so enacted-laws let it be done just once per day.  (@NL7 quotes the security act of 1940, which certainly has been updated, but also still might contain the results of crufty rationales, like this.) There are genuinely different issues between funds and stocks, though: One share of a fund is fundamentally different from one share of stock: There is a finite supply of Company-X-stock, and people are trading that piece of ownership around, and barter to find an mutually-agreeable-price.  But when you buy into a mutual-fund, the mutual-fund ""suddenly has more shares"" -- it takes your money and uses it to buy shares of the underlying stocks (in a ratio equal to its current holdings).  As a consequence: the mutual fund's price isn't determined by two people bartering and agreeing on a price (like stock); there is exactly one sane way to price a mutual fund, and that's the weighted total of its underlying stock.  If you wanted to sell your ownership-of-Mutual-Fund-Z to a friend at 2:34pm, there wouldn't be any bartering, you'd just calculate the value based on the stated-value of the underlying stock at that exact moment. So: there's no inherent reason you can't instantaneously price a mutual fund.  BUT people don't really buy/sell funds to each other -- they go to the fund-manager and essentially make a deposit-or-withdraw.  The fund-manager is only required by law to do it once a day (and perhaps even forbidden from doing it more often?), so that's all they do. [Disclaimer: I know very little about markets and finance. But I recognize answers that are 'just because'.]" As has been pointed out, one isn't cheaper than the other. One may have a lower price per share than the other, but that's not the same thing. Let's pretend that the total market valuation of all the stocks within the index was $10,000,000. (Look, I said let's pretend.) You want to invest $1,000. For the time being, let's also pretend that your purchasing 0.01% of all the stock won't affect prices anywhere. One company splits the index into 10,000 parts worth $1,000 each. The other splits the same index into 10,000,000 parts worth $1 each. Both track the underlying index perfectly. If you invest $1,000 with the first company, you get one part; if you invest $1,000 with the second, you get 1,000 parts. Ignoring spreads, transaction fees and the like, immediately after the purchase, both are worth exactly $1,000 to you. Now, suppose the index goes up 2%. The first company's shares of the index (of which you would have exactly one) are now worth $1,020 each, and the second company's shares of the index (of which you would have exactly 1,000) are worth $1.02 each. In each case, you now have index shares valued at $1,020 for a 2% increase ($1,020 / $1,000 = 1.02 = 102% of your original investment). As you can see, there is no reason to look at the price per share unless you have to buy in terms of whole shares, which is common in the stock market but not necessarily common at all in mutual funds. Because in this case, both funds track the same underlying index, there is no real reason to purchase one rather than the other because you believe they will perform differently. In an ideal world, the two will perform exactly equally. The way to compare the price of mutual funds is to look at the expense ratio. The lower the expense ratio is, the cheaper the fund is, and the less of your money is being eroded every day in fees. Unless you have some very good reason to do differently, that is how you should compare the price of any investment vehicles that track the same underlying commodity (in this case, the S&P 500). "I hope a wall of text with citations qualifies as ""relatively easy."" Many of these studies are worth quoting at length. Long story short, a great deal of research has found that actively-managed funds underperform market indexes and passively-managed funds because of their high turnover and higher fees, among other factors.  Longer answer: Chris is right in stating that survivorship bias presents a problem for such research; however, there are several academic papers that address the survivorship problem, as well as the wider subject of active vs. passive performance. I'll try to provide a brief summary of some of the relevant literature.  The seminal paper that started the debate is Michael Jensen's 1968 paper titled ""The Performance of Mutual Funds in the Period 1945-1964"". This is the paper where Jensen's alpha, the ubiquitous measure of the performance of mutual fund managers, was first defined. Using a dataset of 115 mutual fund managers, Jensen finds that The evidence on mutual fund performance indicates not only that these 115 mutual funds were on average not able to predict security prices well enough to outperform a buy-the-market-and-hold policy, but also that there is very little evidence that any individual fund was able to do significantly better than that which we expected from mere random chance. Although this paper doesn't address problems of survivorship, it's notable because, among other points, it found that managers who actively picked stocks performed worse even when fund expenses were ignored. Since actively-managed funds tend to have higher expenses than passive funds, the actual picture looks even worse for actively managed funds. A more recent paper on the subject, which draws similar conclusions, is Martin Gruber's 1996 paper ""Another puzzle: The growth in actively managed mutual funds"". Gruber calls it ""a puzzle"" that investors still invest in actively-managed funds, given that their performance on average has been inferior to that of index funds. He addresses survivorship bias by tracking funds across the entire sample, including through mergers. Since most mutual funds that disappear are merged into existing funds, he assumes that investors in a fund that disappear choose to continue investing their money in the fund that resulted from the merger. Using this assumption and standard measures of mutual fund performance, Gruber finds that mutual funds underperform an appropriately weighted average of the indices by about 65 basis points per year. Expense ratios for my sample averaged 113 basis points a year. These numbers suggest that active management adds value, but that mutual funds charge the investor more than the value added. Another nice paper is Mark Carhart's 1997 paper ""On persistence in mutual fund performance"" uses a sample free of survivorship bias because it includes ""all known equity funds over this period."" It's worth quoting parts of this paper in full: I demonstrate that expenses have at least a one-for-one negative impact on fund performance, and that turnover also negatively impacts performance. ... Trading reduces performance by approximately 0.95% of the trade's market value.  In reference to expense ratios and other fees, Carhart finds that The investment costs of expense ratios, transaction costs, and load fees all have a direct, negative impact on performance. The study also finds that funds with abnormally high returns last year usually have higher-than-expected returns next year, but not in the following years, because of momentum effects. Lest you think the news is all bad, Russ Wermer's 2000 study ""Mutual fund performance: An empirical decomposition into stock‐picking talent, style, transactions costs, and expenses"" provides an interesting result. He finds that many actively-managed mutual funds hold stocks that outperform the market, even though the net return of the funds themselves underperforms passive funds and the market itself.  On a net-return level, the funds underperform broad market indexes by one percent a year. Of the 2.3% difference between the returns on stock holdings and the net returns of the funds, 0.7% per year is due to the lower average returns of the nonstock holdings of the funds during the period (relative to stocks). The remaining 1.6% per year is split almost evenly between the expense ratios and the transaction costs of the funds. The final paper I'll cite is a 2008 paper by Fama and French (of the Fama-French model covered in business schools) titled, appropriately, ""Mutual Fund Performance"". The paper is pretty technical, and somewhat above my level at this time of night, but the authors state one of their conclusions bluntly quite early on: After costs (that is, in terms of net returns to investors) active investment is a negative sum game.  Emphasis mine. In short, expense ratios, transaction costs, and other fees quickly diminish the returns to active investment. They find that The [value-weight] portfolio of mutual funds that invest primarily in U.S. equities is close to the market portfolio, and estimated before fees and expenses, its alpha is close to zero. Since the [value-weight] portfolio of funds produces an α close to zero in gross returns, the alpha estimated on the net returns to investors is negative by about the amount of fees and expenses. This implies that the higher the fees, the farther alpha decreases below zero. Since actively-managed mutual funds tend to have higher expense ratios than passively-managed index funds, it's safe to say that their net return to the investor is worse than a market index itself. I don't know of any free datasets that would allow you to research this, but one highly-regarded commercial dataset is the CRSP Survivor-Bias-Free US Mutual Fund Database from the Center for Research in Security Prices at the University of Chicago. In financial research, CRSP is one of the ""gold standards"" for historical market data, so if you can access that data (perhaps for a firm or academic institution, if you're affiliated with one that has access), it's one way you could run some numbers yourself." "This is another semantics question.  Again what matters is how the words are commonly used, as the usage came about long before the technical definitions. In this case, when people say ""mutual fund,"" they are often including both unit investment trusts and closed end funds.  Despite the labels the SEC has given in order to differentiate them, I'd say it's common (typical) practice to think of a closed-end fund as a type of mutual fund, rather than a different category altogether.  That's the way I've seen it used, anyway." Behind the scenes, mutual funds and ETFs are very similar.  Both can vary widely in purpose and policies, which is why understanding the prospectus before investing is so important. Since both mutual funds and ETFs cover a wide range of choices, any discussion of management, assets, or expenses when discussing the differences between the two is inaccurate.  Mutual funds and ETFs can both be either managed or index-based,  high expense or low expense, stock or commodity backed. Method of investing When you invest in a mutual fund, you typically set up an account with the mutual fund company and send your money directly to them.  There is often a minimum initial investment required to open your mutual fund account.  Mutual funds sometimes, but not always, have a load, which is a fee that you pay either when you put money in or take money out. An ETF is a mutual fund that is traded like a stock.  To invest, you need a brokerage account that can buy and sell stocks.  When you invest, you pay a transaction fee, just as you would if you purchase a stock.  There isn't really a minimum investment required as there is with a traditional mutual fund, but you usually need to purchase whole shares of the ETF.  There is inherently no load with ETFs. Tax treatment Mutual funds and ETFs are usually taxed the same.  However, capital gain distributions, which are taxable events that occur while you are holding the investment, are more common with mutual funds than they are with ETFs, due to the way that ETFs are structured.  (See Fidelity: ETF versus mutual funds: Tax efficiency for more details.)  That having been said, in an index fund, capital gain distributions are rare anyway, due to the low turnover of the fund. Conclusion When comparing a mutual fund and ETF with similar objectives and expenses and deciding which to choose, it more often comes down to convenience.  If you already have a brokerage account and you are planning on making a one-time investment, an ETF could be more convenient.  If, on the other hand, you have more than the minimum initial investment required and you also plan on making additional regular monthly investments, a traditional no-load mutual fund account could be more convenient and less expensive. This is probably the best, most concise and yet detailed answer to this oft-posed question I've seen on this sub. Have an upvote. Only thing I'd add is that HFs' comparatively more active approach creates a moat vs. mutual funds, which are seen as more long-term, passive investments. This means they can charge fees and have higher expense ratios (though obviously anyone in finance who has been conscious in the last five years knows that this is changing) "This article fails to explain that paper gold doesn't ""necessarily"" guarantee the owner to physical gold.  An index fund tracking the price of gold per ounce guarantees the owner the market value of gold at the termination of the contract.  This keeps markets liquid, and allows investors to diversify into precious metals without the inconvenience of storage and delivery fees.  As long as we are using currency that can be exchanged for gold this shouldn't pose a problem.  If we move to a post currency world of barter and trade, you're better invested in weapons and ammunition." "From http://blog.ometer.com/2008/03/27/index-funds/ , Lots of sensible advisers will tell you to buy index funds, but   importantly, the advice is not simply ""buy index funds.""   There are at least two other critical details: 1) asset allocation   across multiple well-chosen indexes, maintained through regular   rebalancing, and 2) dollar cost averaging (or,   much-more-complex-but-probably-slightly-better, value averaging). The   advice is not to take your single lump sum and buy and hold a   cap-weighted index forever. The advice is an investment   discipline which involves action over time, and an initial   choice among indexes. An index-fund-based   strategy is not completely passive, it involves some active risk   control through rebalancing and averaging. If you'd held a balanced portfolio over the last ten years and rebalanced, and even better if you'd dollar cost averaged, you'd have done fine. Your reaction to the last 10 years incidentally is why I don't believe an almost-all-stocks allocation makes sense for most people even if they're pretty young. More detail in this answer: How would bonds fare if interest rates rose? I think some index fund advocacy and books do people a disservice by focusing too much on the extra cost of active management and why index funds are a good deal.  That point is true, but for most investors, asset allocation, rebalancing, and ""autopilotness"" of their setup are more important to outcome than the expense ratio."