The fiduciary relationship is one of the most fundamental legal relationships, and its importance for both public and private law is increasingly recognized. Fiduciary mandates typically involve one person—the fiduciary—administering the affairs or property of other persons—an individual beneficiary or group of beneficiaries. Yet, as we will demonstrate, this is not the only way fiduciary relationships are structured. Most accounts of fiduciary law oversimplify the law because they exclude a categorically different form of fiduciary relationship. A significant set of fiduciary relationships feature governance mandates in which the fiduciary is charged with pursuing abstract purposes rather than the interests of persons. Indeed, many public and private fiduciary institutions are best understood as being administered on the basis of governance mandates, rendering moot longstanding debates over specification of beneficiaries and requirements of loyalty. The resulting account provides important new insights for core issues in corporate law, administrative law, and constitutional law, among other fields.