What are the core fiduciary duties under ERISA?

Every ERISA fiduciary — for health plans as much as retirement plans — is held to four core duties:

• Loyalty: decisions must be made solely in the interest of participants and beneficiaries, for the exclusive purpose of providing benefits and paying reasonable expenses.
• Prudence: the "prudent expert" standard — act with the care, skill, and diligence a knowledgeable person would use. Process matters more than outcomes: a well-documented, informed decision is prudent even if results disappoint.
• Diversification: primarily an investment duty, but relevant to funded welfare arrangements.
• Adherence to plan documents: follow the written plan terms unless they conflict with ERISA.

In practice, prudence is where health plan fiduciaries face the most scrutiny — vendor selection, fee reasonableness, and claims administration all turn on whether you can demonstrate a careful, documented process.