Civil law or continental law is the predominant system of law in the world, with its origins in Roman law, and sets out a comprehensive system of rules, usually codified, that are applied and interpreted by judges. However, modern systems are descendants of the 19th century codification movement, during which the most important codes (most prominently the Napoleonic Code and the BGB) came into existence.

As discussed in detail below, the civil law systems of Scotland and South Africa are uncodified, and the civil law systems of Scandinavian countries remain largely uncodified.

Civil law is primarily contrasted against common law, which is the legal system developed among Anglo-Saxon people, especially in England.

The original difference is that, historically, common law was law developed by custom, beginning before there were any written laws and continuing to be applied by courts after there were written laws, too, whereas civil law developed out of the Roman law of Justinian's Corpus Juris Civilis (Corpus Iuris Civilis).

In later times, civil law became codified as droit coutumier or customary law that were local compilations of legal principles recognized as normative. Sparked by the age of enlightenment, attempts to codify private law began during the second half of the 18th century (see civil code), but civil codes with a lasting influence were promulgated only after the French Revolution, in jurisdictions such as France (with its Napoleonic Code), Austria (see ABGB), Quebec (see Civil Code of Quebec), Spain (Código Civil), the Netherlands and Germany (see Bürgerliches Gesetzbuch).

However, codification is by no means a defining characteristic of a civil law system, as e.g. the civil law systems of Scandinavian countries remain largely uncodified, whereas common law jurisdictions have frequently codified parts of their laws, e.g. in the U.S. Uniform Commercial Code. There are also mixed systems, such as the laws of Scotland, Louisiana, Quebec, the Philippines, Namibia and South Africa.

Civil and common law system also differ considerably in criminal procedure. In general, the judge in a civil law system plays a more active role in determining the facts of the case. Most civil law countries investigate major crimes using a so-called inquisitorial system. Also, civil law systems rely much more on written argument than oral argument.