In modern federal litigation, these two theories are so often paired together that understanding their relationship is essential.
Much of today's federal agency-delay litigation pleads both a mandamus claim under 28 U.S.C. § 1361 and an Administrative Procedure Act claim under 5 U.S.C. § 706(1) side by side, but the two theories are not identical.
The statutory source of each claim
Mandamus derives from the specific jurisdictional statute discussed elsewhere in this section, historically rooted in common law. The APA claim derives from Congress's more general framework for judicial review of agency action, specifically the provision allowing courts to "compel agency action unlawfully withheld or unreasonably delayed."
Different doctrinal tests, similar practical outcome
Mandamus applies the traditional three-part test (clear right, clear duty, no adequate remedy). The APA claim is typically analyzed through the TRAC factors discussed elsewhere on this site. In practice, courts applying either framework to a delay case often reach similar conclusions, since both are fundamentally asking whether the agency has taken an unreasonably long time to act.
Why petitioners plead both
Pleading both theories in the same complaint gives the court two independent paths to the same relief, reducing the risk that a technical defect in one theory (for example, a dispute over whether the duty is truly "ministerial" for mandamus purposes) will doom the entire case if the APA theory remains available.
Differences in remedy
Courts sometimes note subtle differences in the scope of relief available under each theory, though in unreasonable-delay cases, both generally lead to the same practical outcome: an order directing the agency to complete its review within a specified time.
The bottom line for petitioners
Understanding both frameworks — and pleading them together where appropriate — is now standard practice in federal agency-delay litigation, reflecting decades of case law refining how these two closely related theories work together.