Since there is no world government which all countries recognize to arbitrate disputes over jurisdiction, sovereign powers can find themselves in conflict over which is the more appropriate venue to hear a case, or which country's laws should apply. These conflicts are sometimes resolved de facto by physical factors, such as which country has physical possession of a defendant or property, or sometimes by use of physical police or military force to seize people or property. A country with loose rule of law – for example an absolute monarchy with no independent judiciary – may arbitrarily choose to assert jurisdiction over a case without citing any particular justification. Such assertion can cause problems, such as encouraging other countries to take arbitrary actions over foreign citizens and property, or even provoking skirmishes or armed conflict.
In practice, many countries operate by one or another principles, either in written law or in practice, which communicate when the country will and will not assert jurisdiction:
- treaty jurisdiction — An international treaty explicitly decides the issue.
- territorial principle — A country asserts jurisdiction over people, property, and events taking place on its own territory.
- nationality principle — A country asserts jurisdiction over the conduct of its citizens, anywhere in the world.
- passive personality principle — A country asserts jurisdiction over acts committed against its citizens, anywhere in the world.
- protective principle — A country asserts jurisdiction over issues that affect its interests, such as conspiracies to overthrow its government, or resources critical to its economy (such as access to an international waterway)
- universal jurisdiction — A country asserts jurisdiction over certain acts committed by anyone, anywhere in the world. Usually reserved for exceptionally serious crimes, such as war crimes and crimes against humanity.
Different principles are applied by different countries, and different principles may be applied by the same country in different circumstances. Determination of whether or not a court has jurisdiction to hear a case is the first stage of a conflict of laws proceeding, potentially followed by choice of law to determine which jurisdiction's laws apply. Executive prosecutorial authority and foreign policy also play a role in scope and practical impact of jurisdiction choices.
Any assertion of jurisdiction based on anything other than the territorial principle is known as . Prosecution of a case against an out-of-territory defendant is known as assertion of long-arm jurisdiction.
When a person commits a crime in a foreign country against the laws of that country, usually the host country is responsible for prosecution. The Vienna Convention on Consular Relations requires that the host country notify the foreign embassy, potentially allowing the foreign country to assist in legal defense and monitor conditions of detention. (Most countries protect their citizens against foreign powers in general.)
Foreign diplomats enjoy diplomatic immunity in many countries based on the Vienna Convention on Diplomatic Relations or bilateral agreement, and foreign military personnel may be subject to the jurisdiction of their home country based on a status of forces agreement or Visiting Forces Agreement.
If a person is not physically present in the country which wishes to prosecute a case, that country may either wait until the person enters the national territory, or pursue by legal or extralegal means, and with or without a general extradition treaty. Some countries (like China) prefer to prosecute their own citizens for crimes committed abroad rather than extradite them. Other countries defer to the host country.
When a crime is committed outside the territory of any country, such as in Antarctica, on watercraft in international waters, on aircraft in international airspace, and on spacecraft, jurisdiction is usually determined by the nationality of defendants or victims, or by the flag state of the vessel. This is determined by the admiralty law of the countries involved and in international agreements.