Judicial systems throughout the world generally follow either a civil law or common law method of creating, interpreting. and enforcing laws. In a civil law system, the legislature tends to have more power than the other branches of government because it is in charge of making the laws and the judiciary has little or no authority to interpret or change the laws. In a civil law system, although the legislature makes some of the laws, the judiciary not only has the authority to overturn those laws by finding them unconstitutional, but may also make laws themselves through the concept of stare decis. How a law is declared unconstitutional will depend a great deal on which type of legal system is used in the country in question. In civil law countries, the legislature itself, or a special court, has the authority to declare a law unconstitutional, while, in a common law country, there may be a specific court that decides matters of constitutionality or all courts may determine whether a law is constitutional.
In civil law jurisdictions, such as many of the countries in Europe, the legislature makes the laws and the judiciary simply implements them. The laws are codified into statutes and, when an issue comes before the court, a judge is expected to be able to find the answer within the statutes. In some civil jurisdictions, a special court has been established to review acts of the legislature for compatibility with the constitution. In Germany, for example, the Federal Constitutional Court of Germany is the only court that can rule on the constitutionality of a law passed by the legislature.
In common law jurisdictions, on the other hand, constitutional challenges are more common and laws are declared unconstitutional more frequently. The United Kingdom, as well as many countries that were once under British rule, are common law jurisdictions. The United States, having once been a British colony, is also a common law jurisdiction.
In some common law jurisdictions, there is a special court designated to hear constitutional challenges. In England and Wales, for example, an act or law can only be declared unconstitutional by first applying to the High Court for judicial review. In other countries, all courts have the ability to declare a law unconstitutional.
In the United States, a constitutional challenge may be asserted and a law declared unconstitutional by any court in the country. In practice, although all courts have the power to declare a law unconstitutional, when it actually happens, the case frequently is appealed all the way to the United States Supreme Court. The Supreme Court, being the ultimate authority in the United States, will have the final say regarding the constitutionality of a law.