In a unanimous decision, the Supreme Court has ruled in favor ofparticipants in Edison International's 401(k) plan who claimedcompany fiduciaries violated their duty to monitor threeretail-class mutual funds.

The decision in Tibble vs. Edison International overturns theruling of the 9th Circuit Court of Appeals, which upheld a rulingfrom U.S. District Court for the Central District of California infavor of Edison.

“ERISA's fiduciary duty is derived from the common law oftrusts, which provides that a trustee has a continuingduty—separate and apart from the duty to exercise prudence inselecting investments at the outset—to monitor, and removeimprudent, trust investments,” wrote Justice Stephen Breyer, whodelivered the opinion for the court.