A preliminary injunction is an early, temporary court order restraining or compelling conduct to preserve the status quo until trial, typically to prevent irreparable or hard‑to‑quantify harm. In the UK and Ireland the usual terms are interim or interlocutory injunction (England & Wales, Northern Ireland, Ireland) and interim interdict (Scotland). “Preliminary injunction” is a descriptive expression rather than a statutory label; the governing principles are largely judge‑made.In England & Wales and Northern Ireland, courts apply the American Cyanamid test: a serious question to be tried, adequacy of damages, and the balance of convenience (including preserving the status quo). A cross‑undertaking in damages is normally required; urgent without‑notice applications are possible; breach is contempt of court. Mandatory interim injunctions are granted only with particular caution, usually requiring a stronger merits showing.In Ireland, the Campus Oil principles mirror this approach: a fair question to be tried, adequacy of damages, and balance of convenience, generally with a cross‑undertaking; mandatory orders require a stronger case.In Scotland, interim interdict (or other interim orders) requires a prima facie case and balance of convenience; the court may order caution. Usage and practical effect are broadly consistent across these jurisdictions. Typical contexts include IP, confidentiality, restrictive covenants and commercial disputes.