The Couch Potato strategy thrives on simplicity, but advanced index investors (geeks) should understand what goes on under the hood of ETFs. One of the most important concepts is how ETF shares are created and redeemed. I’ll warn you that this gets a bit technical. But it turns out that this process is the single most important difference between ETFs and index mutual funds.
Let’s begin by looking at how a mutual fund creates new shares (or units). When you make a $2,000 contribution, your money goes directly to the mutual fund’s manager, who uses it to buy more securities. If the fund’s net asset value (NAV) per share is $20, the manager then creates 100 new shares ($2,000 ÷ $20) just for you. This is what’s meant by the term open-end fund: the number of units changes every time money moves in or out.
Closed-end funds, by contrast, do not create or redeem new units. They are launched with a finite number of shares, and if you want to invest in the fund you have to buy your shares from another investor who is willing to sell.