The Principality of Sealand is a micronation on HM Fort Roughs, an offshore platform in the North Sea approximately twelve kilometres off the coast of Suffolk, England. Roughs Tower is a Maunsell Sea Fort that was built by the British in international waters during World War II. Since 1967, the decommissioned Roughs Tower has been occupied and claimed as a sovereign state by the family and associates of Paddy Roy Bates. Bates seized Roughs Tower from a group of pirate radio broadcasters in 1967 with the intention of setting up his own station there. Bates and his associates have repelled incursions from vessels from rival pirate radio stations and the U.K.'s royal navy using firearms and petrol bombs. In 1987, the United Kingdom extended its territorial waters to 12 nautical miles, which places the platform in British territory.

A micronation is a political entity whose representatives claim that they belong to an independent nation or sovereign state, but which lacks legal recognition by any sovereign state. Micronations are classified separately from de facto states and quasi-states; they are also not considered to be autonomous or self-governing as they lack the legal basis in international law for their existence. The activities of micronations are almost always trivial enough to be ignored rather than disputed by the established nations whose territory they claim—referred to in micronationalism as macronations. Several micronations have issued coins, flags, postage stamps, passports, medals and other state-related items, some as a source of revenue. Motivations for the creation of micronations include theoretical experimentation, political protest, artistic expression, personal entertainment and the conduct of criminal activity. The study of micronationalism is known as micropatriology or micropatrology.