Customary International Law

The definition and location of customary international law is a difficult research task. This lesson begins by defining customary international law and placing customary international law into context through historical examples. Two research strategies for locating custom will be introduced. The first strategy is to locate pre-defined custom using a source that discusses state practice that has risen to the level of custom. The second and more complex strategy involves searching directly for evidence of customary international law.

Learning Outcomes

On completion of the lesson, the student will be able to:

1. Define customary international law.
2. Describe a research strategy for locating customary law.
3. List the tools used in customary international law research.