The term lex patriae is Latin for the law of nationality in the Conflict of Laws which is the system of public law applied to any lawsuit where there is a choice to be made between several possibly relevant laws and a different result will be achieved depending on which law is selected.

Explanation

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When a case comes before a court and all the main features of the case are local, the court will apply the lex fori, the prevailing municipal law, to decide the case. But if there are "foreign" elements to the case, the forum court may be obliged under the Conflict of Laws system to consider:

• whether the forum court has jurisdiction to hear the case (see the problem of forum shopping);
• it must then characterise the issues, i.e. allocate the factual basis of the case to its relevant legal classes; and
• then apply the choice of law rules to decide the lex causae, i.e. which law is to be applied to each class.

The lex patriae is a civil law choice of law rule (in some states, the law of habitual residence is used) to test the status and capacity of the parties to the case. For example, suppose that a person with a nationality in Denmark decides to take a "round-the-world" trip. It would be inconvenient if this person's legal status and capacities changed every time he or she entered a new state, e.g. that he or she might be considered an infant or an adult, married or free to marry, bankrupt or creditworthy, etc., depending on the nature of the laws of the place where he or she happened to be. Assuming that there are no public policy issues raised under the relevant lex fori, the lex patriae should apply to define all major issues and so produce an in rem outcome no matter where the case might be litigated. The common law states use a test of lex domicilii (the law of domicile) to determine status and capacity. Because the lex patriae choice of law rule may select the law of a country that contains more than one legal system, there must be rules to determine which of the several possible laws might apply (e.g. a reference to the law of the United States is actually a reference to one of the U.S. states). A suparanational example of this selection process is contained in Article 19 of the Rome Convention:

States with more than one legal system

1. Where a State comprises several territorial units each of which has its own rules of law in respect of contractual obligations, each territorial unit shall be considered as a country for the purposes of identifying the law applicable under this Convention.
2. A State within which different territorial units have their own rules of law in respect of contractual obligations shall not be bound to apply this Convention to conflicts solely between the laws of such units.

See also

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• Lex loci celebrationis
• Lex loci contractus
• Lex loci delicti commissi
• Lex loci solutionis

Conflict of laws | Latin legal phrases