Constitutional law is a body of law dealing with the distribution and exercise of government power.
Not all nation states have codified 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. These may include customary law, conventions, statutory law, judge-made law or international rules and norms, etc.

FUNCTIONS OF CONSTITUTIONS

State and legal structure
Constitutional laws may often be considered second order rulemaking or rules about making rules to exercise power. It governs the relationships between the judiciary, the legislature and the executive with the bodies under its authority. One of the key tasks of constitutions within this context is to indicate hierarchies and relationships of power. For example, in a unitary state, the constitution will vest ultimate authority in one central administration and legislature, and judiciary, though there is often a delegation of power or authority to local or municipal authorities. When a constitution establishes a federal state, it will identify the several levels of government coexisting with exclusive or shared areas of jurisdiction over lawmaking, application and enforcement.

Human rights
Human rights or civil liberties form a crucial part of a country's constitution and govern the rights of the individual against the state. Most jurisdictions, like the United States and France, have a codified constitution, with a bill of rights. A recent example is the Charter of Fundamental Rights of the European Union which was intended to be included in the Treaty establishing a Constitution for Europe that failed to be ratified. Perhaps the most important example is the Universal Declaration of Human Rights under the UN Charter. These are intended to ensure basic political, social and economic standards that a nation state, or intergovernmental body is obliged to provide to its citizens but many do include its governments.

Some countries like the United Kingdom have no entrenched document setting out fundamental rights; in those jurisdictions the constitution is composed of statute, case law and convention. A case named Entick v. Carrington illustrates a constitutional principle deriving from the common law. John Entick's house was searched and ransacked by Sherriff Carrington. Carrington argued that a warrant from a Government minister, the Earl of Halifax was valid authority, even though there was no statutory provision or court order for it. The court, led by Lord Camden stated that.
"The great end, for which men entered into society, was to secure their property. That right is preserved sacred and incommunicable in all instances, where it has not been taken away or abridged by some public law for the good of the whole. By the laws of England, every invasion of private property, be it ever so minute, is a trespass... If no excuse can be found or produced, the silence of the books is an authority against the defendant, and the plaintiff must have judgment.

Inspired by John Locke, the fundamental constitutional principle is that the individual can do anything but that which is forbidden by law, while the state may do nothing but that which is authorized by law.

Inspired by John Locke, the fundamental constitutional principle is that the individual can do anything but that which is forbidden by law, while the state may do nothing but that which is authorized by law.

Inspired by John Locke, the fundamental constitutional principle is that the individual can do anything but that which is forbidden by law, while the state may do nothing but that which is authorized by law.

Legislative procedure
Another main function of constitutions may be to describe the procedure by which parliaments may legislate. For instance, special majorities may be required to alter the constitution. In bicameral legislatures, there may be a process laid out for second or third readings of bills before a new law can enter into force. Alternatively, there may further be requirements for maximum terms that a government can keep power before holding an election.

STUDY OF CONSTITUTIONAL LAW

Constitutional law is a major focus of legal studies and research. For example, most law students in the United States are required to take a class in Constitutional Law during their first year, and several law journals are devoted to the discussion of constitutional issues.

THE RULE OF LAW

The doctrine of the rule of law dictates that government must be conducted according to law. Dicey identified three essential elements of the British Constitution which were indicative of the rule of law:

1. Absence of arbitrary power;

2. Equality before the law;

3. The constitution is a result of the ordinary law of the land.