Precedent in the context of Slaughter-House Cases

A constitution, or supreme law, is the aggregate of fundamental principles or established precedents that constitute the legal basis of a polity, organization or other type of entity, and commonly determines how that entity is to be governed.

When these principles are written down into a single document or set of legal documents, those documents may be said to embody a written constitution; if they are encompassed in a single comprehensive document, it is said to embody a codified constitution. The constitution of the United Kingdom is a notable example of an uncodified constitution; it is instead written in numerous fundamental acts of a legislature, court cases, and treaties.

Law is a set of rules that are created and are enforceable by social or governmental institutions to regulate behavior, with its precise definition a matter of longstanding debate. It has been variously described as a science and as the art of justice. State-enforced laws can be made by a legislature, resulting in statutes; by the executive through decrees and regulations; or by judges' decisions, which form precedent in common law jurisdictions. An autocrat may exercise those functions within their realm. The creation of laws themselves may be influenced by a constitution, written or tacit, and the rights encoded therein. The law shapes politics, economics, history and society in various ways and also serves as a mediator of relations between people.

Legal systems vary between jurisdictions, with their differences analysed in comparative law. In civil law jurisdictions, a legislature or other central body codifies and consolidates the law. In common law systems, judges may make binding case law through precedent, although on occasion this may be overturned by a higher court or the legislature. Religious law is in use in some religious communities and states, and has historically influenced secular law.

An uncodified constitution is a type of constitution where the fundamental rules often take the form of customs, usage, precedent and a variety of statutes and legal instruments. An explicit understanding of such a constitution can be developed through commentary by the judiciary, government committees or legal experts. In such a constitutional system, all these elements may be (or may not be) recognized by courts, legislators, and the bureaucracy as binding upon government and limiting its powers. Such a framework is sometimes imprecisely called an "unwritten constitution"; however, all the elements of an uncodified constitution are typically written down in a variety of official documents, though not codified in a single document. However, there may be truly "unwritten" constitutional conventions which while not usually legally enforceable may hold just as much sway as the letter of the law.

An uncodified constitution has the advantages of elasticity, adaptability, and resilience. A. V. Dicey described the uncodified constitution as "the most flexible polity in existence." A significant disadvantage, however, is that controversies may arise due to different understandings of the usages and customs that form the fundamental provisions of the constitution.

Common law (also known as judicial precedent, judge-made law, or case law) is the body of law primarily developed through judicial decisions rather than statutes. Although common law may incorporate certain statutes, it is largely based on precedent—judicial rulings made in previous similar cases. The presiding judge determines which precedents to apply in deciding each new case.

Common law is deeply rooted in the principle of stare decisis ("to stand by things decided"), where courts follow precedents established by previous decisions. When a similar case has been resolved, courts typically align their reasoning with the precedent set in that decision. However, in a "case of first impression" with no precedent or clear legislative guidance, judges are empowered to resolve the issue and establish new precedent.

Civil law is a legal system rooted in the Roman Empire and was comprehensively codified and disseminated starting in the 19th century, most notably with France's Napoleonic Code (1804) and Germany's Bürgerliches Gesetzbuch (1900). Unlike common law systems, which rely heavily on judicial precedent, civil law systems are characterized by their reliance on legal codes that function as the primary source of law. Today, civil law is the world's most common legal system, practiced in about 150 countries.

The civil law system is often contrasted with the common law system, which originated in medieval England. Whereas the civil law takes the form of legal codes, the common law comes from uncodified case law that arises as a result of judicial decisions, recognizing prior court decisions as legally binding precedent.

Case law, also used interchangeably with common law, is a law that is based on precedents, that is the judicial decisions from previous cases, rather than law based on constitutions, statutes, or regulations. Case law uses the detailed facts of a legal case that have been resolved by courts or similar tribunals. These past decisions are called "case law", or precedent. Stare decisis—a Latin phrase meaning "let the decision stand"—is the principle by which judges are bound to such past decisions, drawing on established judicial authority to formulate their positions.

These judicial interpretations are distinguished from statutory law, which are codes enacted by legislative bodies, and regulatory law, which are established by executive agencies based on statutes. In some jurisdictions, case law can be applied to ongoing adjudication; for example, criminal proceedings or family law.

Jurisprudence constante (French for "stable jurisprudence", or literally, "constant jurisprudence") is a legal doctrine according to which a long series of previous decisions applying a particular legal principle or rule is highly persuasive but not controlling in subsequent cases dealing with similar or identical issues of law. This doctrine is recognized in most civil law jurisdictions as well as in certain mixed jurisdictions such as Louisiana.

The rule of law applied in the jurisprudence constante directly compares with stare decisis. But the Louisiana Supreme Court notes the principal difference between the two legal doctrines: a single court decision can provide sufficient foundation for stare decisis; however, "aseries of adjudicated cases, all in accord, form the basis for jurisprudence constante." Moreover, the Louisiana Court of Appeal has explicitly noted that within Louisiana, jurisprudence constante is merely a secondary source of law, which cannot be authoritative and does not rise to the level of the source of law, which is legislation. Judicial decisions are not intended to be an authoritative source of law, and, thus, the civilian tradition does not recognize the doctrine of stare decisis.

The monarchy of the United Kingdom, commonly referred to as the British monarchy, is the form of government used by the United Kingdom by which a hereditary monarch reigns as the head of state, with their powers regulated by the British constitution. The term may also refer to the role of the royal family within the UK's broader political structure. The monarch since 8 September 2022 is King Charles III, who ascended the throne on the death of Queen Elizabeth II, his mother.

The monarch and their immediate family undertake various official, ceremonial, diplomatic and representational duties. Although formally the monarch has authority over the government—which is known as "His/Her Majesty's Government"—this power may only be used according to laws enacted in Parliament and within constraints of convention and precedent. In practice the monarch's role, including that of Head of the Armed Forces, is limited to functions such as bestowing honours and appointing the prime minister, which are performed in a non-partisan manner. The UK Government has called the monarchy "a unique soft power and diplomatic asset". The Crown also occupies a unique cultural role, serving as an unofficial brand ambassador for British interests and values abroad, increasing tourism at home, and promoting charities throughout civil society.

Landmark court decisions, in present-day common law legal systems, establish precedents that determine a significant new legal principle or concept, or otherwise substantially affect the interpretation of existing law. "Leading case" is commonly used in the United Kingdom and other Commonwealth jurisdictions instead of "landmark case", as used in the United States.

In Commonwealth countries, a reported decision is said to be a leading decision when it has come to be generally regarded as settling the law of the question involved. In 1914, Canadian jurist Augustus Henry Frazer Lefroy said "a 'leading case' [is] one that settles the law upon some important point".

Constitutional law is a body of law which defines the role, powers, and structure of different entities within a state, namely, the executive, the parliament or legislature, and the judiciary; as well as the basic rights of citizens and their relationship with their governments, and in federal countries such as the United States and Canada, the relationship between the central government and state, provincial, or territorial governments.

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 law. Constitutional law deals with the fundamental principles by which the government exercises its authority. In some instances, these principles grant specific powers to the government, such as the power to tax and spend for the welfare of the population. Other times, constitutional principles act to place limits on what the government can do, such as prohibiting the arrest of an individual without sufficient cause.