National law, also called national law system, is a set of laws that governs a country. It includes laws pertaining to the political, legal and economic structure of a country, as well as other relevant rules and regulations.
Constitutional law, on the other hand, is a body of laws that establishes the framework and limits of the governmental power, including checks and balances between government officials and limiting their powers. Most countries have a written Constitution that contains a Bill of Rights and other constitutional provisions.
A number of countries have no written constitution, but instead have a set of Basic laws that guide the way of life in the country. These include England, Canada, New Zealand and Israel.
International law, on the other hand, is the law of nations, which includes laws that govern international and regional organizations as well as individual States. In addition, it includes treaties and other agreements negotiated by governments or multilateral organizations and international bodies.
There are two major ways that international and regional human rights law can influence national systems: Firstly, it can be used as an aid to interpret or develop national law, or incorporated into or derived from the country’s national law. Secondly, international and regional human rights law can be used as a basis for making claims or seeking relief against the governmental authorities.
There are also situations where no conventional or customary international law is applicable. In such cases, general principles that are common to systems of national law can be invoked as a rule of international law.