The international legal system and domestic legal systems are separate entities, despite their frequent interaction. The relationship between the two focuses on: (a) the reception of international law (treaties and custom) into domestic legal orders; and (b) the hierarchy between domestic and international rules.

It is one thing for States to be bound by treaties at the inter-State level (ie between themselves) and it is another for treaties to produce effects in the States’ domestic legal orders. The production of such effects in domestic legal orders depends on the constitutional arrangements of each country. In the UK, this relationship has chiefly been interpreted by the courts.

English law requires that generally in order for treaties adopted by the government to produce effects at the domestic level they must first be implemented by Parliament through an Act or other legislative action.

There are two main constitutional theories for importing treaties and custom into domestic legal orders, namely incorporation and transformation.

Resolutions of the UN Security Council override all other conflicting legislation in the domestic order of States, save if said resolutions are contrary to human rights. Nonetheless, it is up to each country to decide the method by which such resolutions are to become domestic law.