What Is International Customary Law?
1 Video View·Apr 7, 2026
What Is International Customary Law? In this informative video, we break down the concept of international customary law and its significance in the realm of global relations. We'll define what international customary law is and how it operates without formal treaties. Discover the two essential components that contribute to the formation of these unwritten rules: state practice and opinio juris. We will highlight examples of well-established customary laws that countries adhere to, illustrating how these norms shape international interactions.
What is international customary law?
Have you ever wondered how countries agree on rules without signing a formal treaty?
This is where international customary law comes into play.
It's a set of rules that countries follow because they believe these rules are legally binding,
even if they're not written down in a treaty.
International customary law is formed through the consistent practices of countries over time.
For a practice to become a customary law, two key elements must be present.
State practice and opinio juris.
State practice means that countries must consistently follow a particular behavior or rule.
For example, the doctrine of non-refoulement, which prohibits sending someone back to a
country where they might face persecution, is a well-established customary law.
Opinio juris is the belief that this practice is legally binding.
Essentially, countries must act in a way that
shows they believe they are obligated to follow this rule.
This doesn't mean every country has to follow the rule all the time.
What's important is that when they don't follow it, they recognize it as a breach of the law.
Customary international law can cover a wide range of areas,
such as maritime salvage customs that date back to ancient times,
immunity for visiting heads of state and diplomats,
and even peremptory norms like the prohibition of slavery, torture, and genocide.
These norms are so fundamental that they apply to all countries,
even if they didn't agree to them explicitly.
The International Court of Justice, the main judicial body of the United Nations,
recognizes customary international law as one of the sources of international law.
This means that even if a country hasn't signed a specific treaty,
it can still be bound by customary laws that have been widely accepted and practiced.
In summary, international customary law is about the unwritten rules that countries follow
because they believe they are legally obligated to do so,
based on consistent practices and a shared understanding
of what is right and wrong in the international community.