The concept of national law is the idea that each country has its own legal system, and the rules that govern it are the laws of that nation. National laws are the basis for most of our day-to-day lives. For example, all citizens must obey traffic rules to avoid accidents, and countries sign international treaties to facilitate things like trade and military cooperation.

When a nation signs an international treaty it essentially creates a new set of laws. These become a part of the national legal system and can be enforced by the courts. In fact, some treaties are so important that a State will include them in its constitutions. These are called constitutional treaties.

In other cases, States may incorporate international treaty norms into its domestic law through a process called ‘transformation’. The first method, called general transformation, gives a treaty domestic effect without the need for legislative action beyond ratification. The other method, called special transformation, requires that legislation be enacted to give the treaty domestic effect.

Some academics have claimed that there is a third category of law, called ‘a-national law’ or the lex mercatoria, which is independent of the law of nation states and is based on spontaneous trade usages. However, critics point out that detaching a body of law from the concept of a nation is little more than wishful thinking. In addition, many a-national rules are merely the result of legal harmonization and are therefore not truly a-national.