Customary international law and general principles of law are challenging to research because they are documented in a wide variety of sources. Researchers unfamiliar with the area should consult one of the general works on international law listed in the 'Books' tab, or consult one of the resources listed on this page to gain an understanding of the general principles before proceeding to more specific research.
The elements of customary international law include:
1. Widespread repetition by States of similar international acts over time (State practice).
2. Acts must occur out of sense of obligation (opinio juris).
3. Acts must be taken by a significant number of States and not be rejected by a significant number of States.
For information on customary international law see the resources listed below, or the relevant chapters in the treatises listed in the books tab
Particularly comments of §102, 'b' through 'e', discussing the notion of custom.
Also available through Westlaw Canada via the Restatements and Principles of the Law - Combined (REST) database. Subscription required, available for UofT law students.
Anthea Elizabeth Roberts, “Traditional and Modern Approaches to Customary International Law: A Reconciliation” (2001) 95 Am. J. Int'l L. 757.
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