Sources of environmental law
Articulating environmental statutory texts in Europe

International law has three main sources:

• international treaties or conventions ;

• international custom, which derives from the actual practice of States, accompanied by opinio juris, i.e. the conviction of States that they are complying with a genuine rule of law and not mere usage. International custom differs from national custom, which is based on long-standing, constant and notorious usage that is both secondary and inferior to national laws and regulations;

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