Based on analysis of a large number of recent domestic court cases on matters of customary international law (2000–2014), this article demonstrates that, rather similar to the International Court of Justice, domestic courts do not normally identify customary norms of customary international law on the basis of the textbook method of ascertaining a general practice accepted as law. Rather, they tend to outsource the determination of custom to treaties, non-binding documents, doctrine or international judicial practice. Sometimes, it appears that domestic courts simply assert, without citing persuasive practice authority, the existence of a customary norm. In rare cases, however, domestic courts do engage in extensive analysis.

中文翻译：

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确定习惯国际法：对国内法院使用方法的调查

本文基于对近期国内法院关于习惯国际法事务的大量案例（2000-2014 年）的分析，表明国内法院与国际法院相当相似，通常不识别习惯国际法的习惯规范。以教科书方法为基础，确定普遍接受为法律的惯例。相反，他们倾向于将习惯的决定外包给条约、非约束性文件、学说或国际司法实践。有时，似乎国内法院只是断言存在习惯规范，而没有引用具有说服力的实践权威。然而，在极少数情况下，国内法院确实会进行广泛的分析。