Most commonly constitutional law is the law of these foundational laws, customs, and constitutional conventions in regard to nation-states. Not all nation-states have constitutions, though all such states have a jus commune, or law of the land, that may consist of a variety of imperative and consensual rules, that may be customary law, oral law and written law that apply in the various jurisdictions of such state. Of those nation-states that do have constitutions, not all are considered strictly written constitutions, as the laws that govern such issues may not be consolidated into one single constitution document or instrument. The constitutional law may be a matter of interpreting a variety of text which may also be informed by history, custom and unwritten constitutional conventions . Compare, for example, the written Constitution of the United States with British constitutional law, which arises from multiple sources including the Magna Carta, the common law, and other customary sources. In some countries the constitution is known as the Basic Law.
Constitutional laws may often be considered second order rulemaking or rules about making rules. Generally speaking constitutions may be of a federal type (see: federal state), in which several levels of government coexist with exclusive or shared areas of jurisdiction over lawmaking, application and enforcement. Two example of these kinds of contitutions are the United States and the European Union. Constitutional laws may also be of a unitary type (see: unitary state) where the powers of government rest in one central administration and legislature, though in unitary constitutional states, they is often a delegation of power or authority to local or municipal authorities, however the central legislature retains the right to recall its authority at anytime.
Other types of constitutional law also exist, such as confederations, in which a group of nation-states each with its own sovereignty create a common body to deal with certain common issues in which limited powers are transferred to the confederation authority, common in custom unions, this was also the first form of government created by the thirteen colonies after the American Revolution in the Articles of Confederation.