This Mutual Fund Giant Is Now Offering a Zero-Fee Index Fund. So What’s the Catch?

Retirement giant Fidelity wants to let you invest for free. But should you?

Earlier this month the Boston-based mutual fund company launched Fidelity Zero Total Market Index Fund and the Fidelity Zero International Index Fund, two new index funds Fidelity says will charge investors nothing.

The new funds -- designed to give investors broad-based exposure to U.S. and international stocks, respectively -- are the result of a years' long price war between Fidelity and other big U.S.