Law is a set of rules that are enforced by social or governmental institutions to regulate behavior. The precise definition is a matter of ongoing debate, but law is generally considered to include statutes and regulations, executive orders, judicial decisions, and binding contracts. The word may also refer to the rules of a particular jurisdiction or the principles underlying its government or justice system. Laws may be imposed by a group legislature or individual legislator, resulting in statutes; by the executive, with decrees and regulations; or by judges in common law jurisdictions through precedent. Private individuals may also create legally binding contracts and arbitration agreements, which are alternatives to standard court litigation.

In common law systems, the judgments of courts are treated as laws on equal footing with legislative statutes and executive regulations. This is based on the principle of stare decisis, whereby decisions of higher courts bind lower courts to ensure consistency of results. This is a major strength of common law systems, and a key reason why they are preferred by commercial parties.

Many countries have a written constitution, which defines the basic rules of the country. The United States, for example, has a written constitution that contains 395 articles, 12 schedules and numerous amendments. Other countries have a largely unwritten constitution or legal system, while some rely on an unwritten code of conduct, or on a system of adjudication with limited or no formal legislation. For example, Israel has no written constitution, but it relies on the Supreme Court to review and overturn legislative and executive decisions.

Most of the world’s law is created by a system of case law, with judge-made decisions being legally binding and creating precedent. The development of law through the case-law process is often influenced by the felt necessities of the time, prevalent moral and political theories, intuitions of public policy, avowed or unconscious, and even the prejudices of individual judges. This makes law a social product rather than an intellectual product, and a good legal system must be sensitive to these influences in developing its laws.

The practice of law is usually overseen by a government or independent regulating body such as a bar association or bar council. Modern lawyers achieve a distinct professional identity through specified legal procedures (e.g. passing a qualifying examination), and are constituted in office by legal forms of appointment (being admitted to the bar).

The law of a particular jurisdiction may be determined by statute or regulation, but is more likely to be established by precedent or by judicial decisions. The latter are often lengthy, and include detailed rationales and policies that can be balanced with judgment in future cases, as opposed to the bright-line rules of a statute. Laws relating to specific activities or industries are called regulatory law. Examples include banking and financial regulation, as well as the laws governing water, energy and telecoms. This type of law aims to protect consumers, regulate the business practices of monopolies, and provide a level playing field between businesses.