Lex causae

In the conflict of laws, lex causae (Latin: lex + causa, "cause [for the] law") is the law or laws chosen by the forum court from among the relevant legal systems to arrive at its judgment of an international or interjurisdictional case. The term refers to the usage of particular local laws as the basis or "cause" for the ruling, which would itself become part of referenced legal canon.

Conflict of laws regulates all lawsuits involving foreign law if the outcome of a legal action will differ based on the laws that are applied. Once the forum court has ruled that it has jurisdiction to hear the case, it must then decide among the possible laws to be applied.

When the parties and the causes of action are local, the court will apply the lex fori, the prevailing municipal law. If there are foreign elements to the case, the forum court should, under the conflict of laws, consider if it should apply one or more foreign laws.

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