Service by publication is the court‑authorised giving of notice of proceedings by advertising (for example in a newspaper or official gazette/website) when the respondent cannot, with reasonable diligence, be served by conventional means. It is exceptional and used to enable claims, family applications or other civil proceedings to progress where addresses are unknown or a party is evading service, while safeguarding procedural fairness.In England and Wales, the Civil Procedure Rules permit “service by an alternative method” on application, which may include advertisement or online posting; the order specifies the steps and when service is deemed effected. Northern Ireland adopts a similar approach under its Rules of the Court of Judicature, commonly described as substituted service.In Scotland, the nearest equivalent is edictal citation: citation by advertisement (often in the Edinburgh Gazette and, where appropriate, a local paper) authorised by the Court of Session or sheriff court on evidence of diligent inquiry.In Ireland, the Rules of the Superior, Circuit and District Courts provide for substituted service, frequently by newspaper advertisement and posting to the last‑known address, where personal service is impracticable.Across all jurisdictions, court permission is normally required, proof of reasonable efforts to trace the respondent is essential, and publication must be reasonably likely to come to their attention.