Definition
A preliminary injunction is a court order issued before final judgment that requires a party to refrain from — or occasionally to perform — a specified act while litigation is pending. It is an interim remedy, designed to preserve the status quo and prevent irreparable harm during the period between the filing of suit and a final resolution on the merits.
A preliminary injunction is more powerful than a temporary restraining order (TRO), which is issued on an emergency basis without notice to the opposing party and expires quickly. A preliminary injunction, by contrast, is entered only after notice to the adverse party and an opportunity for hearing, and it remains in effect until dissolved, modified, or superseded by final judgment.
In federal practice, preliminary injunctions are governed by Rule 65(a) of the Federal Rules of Civil Procedure. The movant bears the burden of satisfying a multi-factor test. Under the standard established in Winter v. Natural Resources Defense Council (2008), a federal court will issue a preliminary injunction only when the movant demonstrates: (1) likelihood of success on the merits; (2) likelihood of irreparable harm in the absence of preliminary relief; (3) that the balance of equities tips in the movant's favor; and (4) that an injunction is in the public interest. Rule 65(c) additionally requires the movant to post a security bond to compensate the restrained party for wrongful injunction damages if the court later determines the injunction was improperly granted.
Common Language
Wiktionary: "A court order prohibiting a party to litigation from carrying on a course of action until a trial has determined whether the course of action is proper."
The Wiktionary definition is broadly accurate but misleading in two respects. First, it suggests preliminary injunctions are exclusively prohibitory; in practice, mandatory preliminary injunctions — requiring affirmative action — are also available, though courts grant them with greater reluctance. Second, "until a trial has determined" overstates the connection to trial; many cases settle or are resolved on motions after a preliminary injunction issues, and the injunction governs the entire interim period regardless of whether trial actually occurs. The legal term carries the additional weight of a formal multi-factor test that the plain English framing does not convey.
Common Confusion
PRELIMINARY INJUNCTION vs. TEMPORARY RESTRAINING ORDER (TRO): These terms are frequently conflated, and historical sources often treat them interchangeably or inconsistently. The operative distinctions are notice, duration, and the opportunity to be heard. A TRO may issue ex parte — without notice to the adverse party — when immediate irreparable injury would result before notice can be given. A preliminary injunction requires notice and a hearing. TROs are short-lived by design (typically capped at fourteen days under FRCP 65(a)(2)); preliminary injunctions can remain effective for the life of the litigation.
PRELIMINARY INJUNCTION vs. PERMANENT INJUNCTION: A permanent injunction is a final remedy entered after full adjudication on the merits. A preliminary injunction is expressly provisional — the court's ruling on the preliminary injunction motion does not determine the merits of the underlying claim, and findings made at that stage do not bind the parties at trial.
Core Elements
The Winter four-factor test governs federal courts and has been widely adopted by state courts. Each factor is independently significant; no single factor is automatically dispositive, though courts have differed on whether the factors are strictly conjunctive or admit of sliding-scale balancing.
1. Likelihood of success on the merits. The movant must show more than a mere possibility of prevailing. This is often the dispositive inquiry. The court conducts a preliminary examination of the merits without finally resolving them.
2. Likelihood of irreparable harm. The harm must be likely, not merely possible, and it must be the kind that money damages at final judgment cannot adequately remedy. Delay in seeking the injunction can undermine this showing.
3. Balance of equities. The court weighs the harm to the movant if relief is denied against the harm to the respondent if relief is granted. A significant asymmetry in either direction can tip the analysis.
4. Public interest. Particularly significant in cases involving government defendants or matters of broad public concern. Courts will not issue injunctive relief that would disserve the public even if the private-party factors favor the movant.
Why It Matters in Research
Corpus researchers face several distinct challenges with this term.
The four-factor test is modern. Prior to Winter (2008), many federal circuits applied a more flexible balancing test that permitted a "sliding scale" — a strong showing on irreparable harm could compensate for a weaker showing on the merits. Post-Winter sources reflect the stricter conjunctive standard. Researchers relying on pre-2008 secondary sources or circuit-level decisions from that era must account for this doctrinal shift. Cases analyzing the older "probability of success" or "serious questions" standards may no longer accurately reflect governing law in federal courts.
The bond requirement has a separate doctrinal life. Rule 65(c) security and wrongful injunction damages are frequently analyzed independently of the four-factor test. Researchers following remedies questions should trace the bond issue to remedies_27, not simply to the injunction analysis in civpro_115.
State courts are not uniform. Many states follow something close to the Winter framework, but formulations vary — some expressly retain sliding-scale analysis, and some require a higher or lower threshold for the merits showing. Sources analyzing state-court injunctions should be verified against current state procedural rules.
Mandatory vs. prohibitory injunctions. The distinction matters for the applicable standard of scrutiny. Historical sources often discuss only prohibitory injunctions (restraining action), and a researcher looking for authority on mandatory preliminary injunctions (compelling affirmative acts) will find the case law sparser and the standards more demanding.
The term appears throughout equity practice materials predating the merger of law and equity. In pre-merger sources, injunctions were exclusively a creature of equity courts. Researchers in historical federal materials (pre-1938 FRCP) will encounter the term in that context, where procedural mechanics differed substantially.
Historical Dictionary Support
Black's Law Dictionary provides the core historical definition: an injunction granted at the institution of a suit, restraining the defendant from doing or continuing a disputed act, which may be discharged or made perpetual depending on the outcome. This formulation captures the essential structure — interim restraint tied to an unresolved underlying controversy — and has remained essentially accurate across editions.
The Black's definition reflects the classical equity-court framework, where the preliminary injunction was understood primarily as a preservation device: holding the situation static until rights could be determined. This orientation is still accurate but understates the contemporary four-factor analytical structure, which requires courts to affirmatively assess the merits, harm, equities, and public interest rather than simply asking whether a genuine dispute exists.
Historical dictionaries generally do not address the bond requirement as part of the definition of preliminary injunction, treating security as a procedural rather than definitional matter. Researchers should not assume from a historical definition that no security obligation exists; the bond requirement has deep roots in equity practice even if it was not foregrounded in dictionary treatments.
Note: The Black's source material in the record contains an apparent typesetting artifact (language about "a female who has within her ovary or womb a fecundated germ"), which is unrelated to the preliminary injunction entry and appears to be a typographic intrusion from an adjacent entry. It carries no interpretive weight.
Jurisdictional Note
Federal courts apply the Winter four-factor test. State courts vary: many adopt equivalent multi-factor frameworks, but formulations — particularly the weight given to likelihood of success versus irreparable harm — differ by jurisdiction. Some states expressly permit sliding-scale balancing that federal courts have moved away from. Researchers analyzing state preliminary injunction practice should verify the controlling standard in the specific jurisdiction rather than importing the federal framework wholesale.
Encyclopedia Cross-Reference
civpro_115: Preliminary Injunctions — Rule 65(a) and the Winter v. NRDC Factors (The Law Mind Civil Procedure & Evidence Encyclopedia) — primary reference for the federal procedural framework, notice requirements, and four-factor analysis.
remedies_27: Injunction Bonds — Rule 65(c), Amount, and Wrongful Injunction Damages (The Law Mind Remedies & Equity Encyclopedia) — essential companion for the security requirement and liability exposure when an injunction is later found to have been improperly granted.