Under ERISA, retirement plan fiduciaries must ensure fees paid from plan assets are reasonable for the services provided. While the lowest fee is not required, fiduciaries should understand all fees, have a fee policy statement, review annual fee disclosures, conduct periodic benchmarking studies, and issue RFPs for services every 5 years to demonstrate reasonable fees. When selecting mutual funds, fiduciaries must consider overall costs and revenue sharing, not just share class, and show a prudent process for evaluations.