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.

Historically, a civil law is the group of legal ideas and systems ultimately derived from the Corpus Juris Civilis, but heavily overlain by Napoleonic, Germanic, canonical, feudal, and local practices, as well as doctrinal strains such as natural law, codification, and legal positivism.

Conceptually, civil law proceeds from abstractions, formulates general principles, and distinguishes substantive rules from procedural rules. It holds case law secondary and subordinate to statutory law. Civil law is often paired with the inquisitorial system, but the terms are not synonymous. There are key differences between a statute and a code. The most pronounced features of civil systems are their legal codes, with concise and broadly applicable texts that typically avoid factually specific scenarios. The short articles in a civil law code deal in generalities and stand in contrast with ordinary statutes, which are often very long and very detailed.

The civil law system is the most widespread system of law in the world, in force in various forms in about 150 countries.

Civil law is sometimes referred to as neo-Roman law, Romano-Germanic law or Continental law. The expression "civil law" is a translation of Latin jus civile, or "citizens' law", which was the late imperial term for its legal system, as opposed to the laws governing conquered peoples (jus gentium); hence, the Justinian Code's title Corpus Juris Civilis. Civil law practitioners, however, traditionally refer to their system in a broad sense as jus commune. It draws heavily from Roman law, arguably the most intricate legal system before the modern era.^{[citation needed]}

In civil law legal systems where codes exist, the primary source of law is the law code, a systematic collection of interrelated articles, arranged by subject matter in some pre-specified order. Codes explain the principles of law, rights, and entitlements, and how basic legal mechanisms work. The purpose of codification is to provide all citizens with manners and a written collection of the laws which apply to them and which judges must follow. Law codes are laws enacted by a legislature, even if they are in general much longer than other laws. Rather than a compendium of statutes or catalog of case law, the code sets out general principles as rules of law.

While the typical French-speaking supreme court decision is short, concise, and devoid of explanation or justification, in Germanic Europe, the supreme courts can and do tend to write more verbose opinions, supported by legal reasoning. A line of similar case decisions, while not precedent per se, constitute jurisprudence constante. While civil law jurisdictions place little reliance on court decisions, they tend to generate a phenomenal number of reported legal opinions. However, this tends to be uncontrolled, since there is no statutory requirement that any case be reported or published in a law report, except for the councils of state and constitutional courts. Except for the highest courts, all publication of legal opinions is unofficial or commercial.