In the U.S., whenever a mutual fund realizes a capital gain that is not balanced by a realized loss, the mutual fund must "distribute" the capital gains to its shareholders and the shareholders must pay capital gains taxes on the amount of the gain (unless such investment is held in an individual retirement account), even if the distribution is reinvested. This can happen whenever the mutual fund sells portfolio securities, whether to reallocate its investments or to fund shareholder redemptions. In contrast, ETFs are not redeemed by investors; any investor who wants to liquidate generally would sell the ETF shares on the secondary market, so investors generally only realize capital gains when they sell their own shares for a gain.