Mandamus directs a lower court to act, or to refrain from acting. It is not a substitute for appeal and is granted rarely.
The usual standard. No other adequate means to obtain relief; a right to the writ that is clear and indisputable; and the issuing court’s satisfaction, in its discretion, that the writ is appropriate. Some formulations add whether the order is an oft-repeated error, and whether it raises new and important problems.
Where it succeeds. Orders compelling disclosure of privileged material, where the harm cannot be undone; refusals to enforce forum selection or arbitration provisions in some circuits; orders exceeding the court’s power altogether; and disqualification or recusal in narrow circumstances.
Where it fails. Disagreement with a discretionary ruling, however strongly held. Mandamus corrects a judicial usurpation of power or a clear abuse of discretion, not ordinary error.
Procedure. The petition is filed in the appellate court, naming the trial judge as respondent by convention while the real party in interest defends. The appellate court may deny without a response, or call for an answer, which is itself a meaningful signal.
Practical consequence. Because relief is rare, a petition should be reserved for orders with irreversible consequences and should be filed immediately; delay defeats the argument that no adequate alternative exists.