A preliminary injunction orders a party to do or stop doing something while the case proceeds. Courts generally weigh four factors: likelihood of success on the merits, irreparable harm without the injunction, the balance of hardships, and the public interest.

Irreparable harm is where most applications fail. Harm compensable in money is by definition not irreparable, so a claim that amounts to lost profits is poorly suited to injunctive relief. Loss of goodwill, disclosure of trade secrets, and breach of a non-compete are argued as irreparable precisely because the loss resists measurement.

Speed matters twice over. A party that waits months before applying undercuts its own claim of urgency. And because the motion is decided on limited evidence in a short window, what can be assembled in the first two weeks often determines the result — and the result often determines the case, since the losing party’s position frequently becomes untenable regardless of the eventual merits.

A temporary restraining order is the shorter-term version, sometimes granted without notice, lasting only until a full hearing can be held.