The English legal system is based on the common law. Consistency and predictability are assured by prior decisions of the courts on similar matters establishing judicial precedent. The continuing role of the courts is to apply and develop the common law. Statute law is created by Parliament and takes precedence over common law, Parliament being the supreme legal authority of the United Kingdom. This supremacy has been affected by the UK's membership of the European Union (EU), with European Law taking precedence over British Acts of Parliament (although it is still thought possible by many that Parliament could reassert its supremacy if it should so choose).

The alternative legal tradition in most of Europe is derived originally from the legal system of Ancient Rome, also known as Civil Law (the latter not to be confused with English ‘civil law’ which refers to non-criminal legal matters – see below). Over the centuries the code developed as a body of international law, the ius commune and was later codified in many countries as their own national expression of law. In contrast to common law precedent, consistency is achieved by judicial application and interpretation of the code, rather than of prior case law decisions.

The United Kingdom exported the English legal system to its colonies, including the United States, and the countries of the Commonwealth. Most retained it after independence. By similar colonial expansion many countries of Europe established Roman law as the predominant legal system.