Sovereigns sojourning in their official capacity in foreign countries are exempt from local jurisdiction. This principle is based, not merely upon courtesy, but also upon convenience and necessity. The sovereign represents the state, and therefore cannot be subjected to the jurisdiction of another state without waiving the sovereignty, and in so far depriving the state of one of its essential qualities. Nor can the visiting sovereign exercise any authority which would infringe the sovereign powers of the state in which he is. The visiting sovereign can only claim immunity for such action as is in accord with the necessities of his convenient sojourn. He, his retinue, and effects, are exempt from civil and criminal jurisdiction. He is free from taxes, duties, police and administrative regulations. In the case of Vavasseur _v._ Krupp, 1878, it was decided that infringement of the patent law did not constitute a ground for suit against a sovereign. In this case Vavasseur brought action against Krupp for infringement of patent on shells in custody of the agents of the Mikado of Japan. The action resulted in an injunction preventing removal of the shells to the Mikado's ships, but on application of the Mikado to remove the shells as his property, the court held that, even if the property in question infringed a patent, the Mikado could not be sued and his property could not be held.[179] The principle that the sovereign is free from suit has frequently been decided by the courts of various countries. A sovereign sojourning in a foreign state cannot, however, set up his courts and execute judgment; such functions belong to his territorial courts. Criminals in his retinue must be sent home for trial. While the sovereign's _hôtel_ or place of residence while abroad is exempt from local jurisdiction, the sovereign is not justified in allowing the _hôtel_ to become an asylum for others than members of his retinue. On demand he must give up such refugees. In case the sovereign does not observe this principle or commits acts liable to endanger the peace of the foreign state, the authorities may invite him to depart, or if necessary expel him by force.
The sovereign may, in his private capacity, hold property and become party to a suit like any citizen.[180] A sovereign may travel _incognito_, and is then entitled only to the recognition accorded to the rank which he assumes. He can, however, assert his sovereign capacity and obtain its immunities at any time should he deem it proper.