555 U.S. 7 (2008) (U.S. Supreme Court)
Winter v. Natural Resources Defense Council, Inc.
Whether the Ninth Circuit erred by affirming a preliminary injunction under NEPA based on a mere possibility of irreparable harm and without properly balancing the equities and public interest in light of the Navy's national security and training needs.
A plaintiff seeking a preliminary injunction must establish (1) a likelihood of success on the merits, (2) a likelihood of suffering irreparable harm absent preliminary relief, (3) that the balance of equities tips in the plaintiff's favor, and (4) that an injunction is in the public interest. A preliminary injunction is an extraordinary remedy never awarded as of right. NEPA is a procedural statute; a likely NEPA violation does not automatically entitle a plaintiff to injunctive relief—courts must apply traditional equitable principles and weigh competing public interests.
The Supreme Court reversed the Ninth Circuit and vacated the preliminary injunction. The plaintiffs did not demonstrate a likelihood of irreparable harm, and the balance of equities and the public interest strongly favored allowing the Navy's training exercises to proceed without the court-imposed restrictions.
Winter is the modern touchstone for preliminary injunctions in federal court. It (1) clarifies that a likelihood—not a mere possibility—of irreparable harm is required, (2) emphasizes that injunctions are extraordinary and not automatic even when a plaintiff shows likelihood of success, and (3) requires explicit balancing of equities and consideration of the public interest. The decision reshaped Ninth Circuit practice and has been repeatedly cited across substantive fields. For environmental and administrative law, Winter underscores that NEPA is procedural and that remedies must account for competing public interests, including national security. For remedies more broadly, it sits alongside eBay Inc. v. MercExchange (permanent injunctions) and Munaf v. Geren (extraordinary relief) and informs later cases like Nken v. Holder (stays), forming a coherent modern framework for equitable interim relief.