The territorial principle (also territoriality principle) is a principle of public international law under which a sovereign state can prosecute criminal offences that are committed within its borders. The principle also bars states from exercising jurisdiction beyond their borders, unless they have jurisdiction under other principles such as the principle of nationality, the passive personality principle, the protective principle, and possibly universal jurisdiction.
The Lotus case was a key court ruling on the territoriality principle. In 1926, a French vessel collided with a Turkish vessel, causing the death of several Turkish nationals. The Permanent Court of International Justice ruled, by a bare majority, that Turkey had jurisdiction to try the French naval lieutenant for criminal negligence, even though the incident happened beyond Turkey's boundaries. This case extended the territoriality principle to cover cases that happen outside a state's boundaries, but have a substantial effect on the state's interests or involve its citizens.
Questions have surfaced regarding how the territoriality principle applies, with the rise of globalization and the Internet. The applicability of this principle also was in question, with the case against Augusto Pinochet and other cases of transnational justice.