Throughout the world, there are two basic types of judicial systems — civil law and common law. Although there are a number of countries that have evolved to use what can best be described as hybrid legal systems, all legal systems have a basis in common law or civil law. In short, a civil law system is based on statutory law, while a common law system is based on legal precedents. Unlike a civil law system, judges in a common law legal system actually make law instead of just implementing the law.
The roots of the common law legal systems can be traced back to the first common law system created in England during the Middle Ages. Today, most countries that once had ties to England, including the United States, Australia, New Zealand, and Hong Kong, to name a few, operate under common law. Aside from Great Britain, the majority of the countries in Europe operate under a version of civil law modeled after the Roman legal system created centuries ago.
In a common law system, the law is created by precedents set after judges decide actual cases. When a judge hears a case that has a new issue in it, the judge makes a decision regarding the issue in the case. That decision then becomes a precedent that must be followed by other courts with equal standing within the legal system. The precedent remains law unless and until a higher court overturns the decision. The practice of following decisions made by other courts for similar issues is known as stare decisis.
In stark contrast to the concept of stare decisis and precedent found in a common law system, decisions in a civil law system are to be made based on a corresponding statute, in theory. In a civil law system, the legislative or executive branch makes the laws and courts are simply required to follow the laws as they have been written. A judge, therefore, in a civil law system, has considerably less authority or autonomy than a judge in a system based on common law.
Judges in a common law system are, of course, required to follow the laws of precedent; however, a judge may go against precedent if he or she feels strongly that the existing precedent is wrong. Cases that come before a judge in a common law legal system that have a new issue are referred to as an "issue of first impression." When a judge is faced with an issue of first impression, he or she will look to other similar cases and the reasoning used in those cases, and then apply it to the case at hand.