The Case of the Dean of St Asaph, formally R v Shipley, was the 1784 trial of William Davies Shipley, the Dean of St Asaph, for seditious libel. In the aftermath of the American War of Independence, electoral reform had become a substantial issue, and William Pitt the Younger attempted to bring a Bill before Parliament to reform the electoral system. In its support Shipley republished a pamphlet written by his brother-in-law, Sir William Jones, which noted the defects of the existing system and argued in support of Pitt's reforms. Thomas FitzMaurice, the brother of British Prime Minister Earl of Shelburne, reacted by indicting Shipley for seditious libel, a criminal offence which acted as "the government's chief weapon against criticism", since merely publishing something that an individual judge interpreted as libel was enough for a conviction; a jury was prohibited from deciding whether the material was actually libellous. The law was widely seen as unfair, and a Society for Constitutional Information was formed to pay Shipley's legal fees. With financial backing from the society Shipley was able to secure the services of Thomas Erskine KC as his barrister.

William Davies Shipley was an Anglican priest who served as Dean of St Asaph for nearly 52 years, from 27 May 1774 until his death. In a legal cause célèbre which became known as the Case of the Dean of St Asaph, he was tried and convicted on a charge of seditious libel in August 1784, but was discharged by the Court of King's Bench a few months later without being punished.