Offer your thoughts or opinion on the input financial query or topic using your financial background.

What differentiates index funds and ETFs?
I think that assuming that you're not looking to trade the fund, an index Mutual Fund is a better overall value than an ETF. The cost difference is negligible, and the ability to dollar-cost average future contributions with no transaction costs. You also have to be careful with ETFs; the spreads are wide on a low-volume fund and some ETFs are going more exotic things that can burn a novice investor. Track two similar funds (say Vanguard Total Stock Market: VTSMX and Vanguard Total Stock Market ETF: VTI), you'll see that they track similarly.  If you are a more sophisticated investor, ETFs give you the ability to use options to hedge against declines in value without having to incur capital gains from the sale of the fund. (ie. 20 years from now, can use puts to make up for short-term losses instead of selling shares to avoid losses)  For most retail investors, I think you really need to justify using ETFs versus mutual funds. If anything, the limitations of mutual funds (no intra-day trading, no options, etc) discourage speculative behavior that is ultimately not in your best interest. EDIT: Since this answer was written, many brokers have begun offering a suite of ETFs with no transaction fees. That may push the cost equation over to support Index ETFs over Index Mutual Funds, particularly if it's a big ETF with narrow spreads..