Some mutual funds charge sales commissions for trading fund shares. These commissions are also known as the "sales loads," and they are expressed as a percentage of the transaction value. Class A mutual fund shares charge a "front-end load" as you buy them. Class B mutual fund shares charge a "back-end load" as you sell them. When possible, you may want to look for "no-load" funds that don't charge any sales commission. Sales loads are different from expense fees, which all funds charge in order to pay the fund managers.