A constitutional court is a high court that deals primarily with constitutional law. Its main authority is to rule on whether laws that are challenged are in fact unconstitutional, i.e. whether they conflict with constitutionally established rules, rights, and freedoms, among other things.
Prior to 1919, the United States, Canada and Australia had adopted the concept of judicial review by their courts, following shared principles of their similar common law legal systems, which they, in turn, had inherited from British legal practice (the United Kingdom does not have a codified constitution and judicial review of primary legislation is prohibited). The Parthenopean Republic's constitution of 1799, written by Mario Pagano, envisaged an organ of magistrates reviewing constitutional law, the eforato, but lasted only 6 months. The 1776 Constitution of Pennsylvania and 1777 Constitution of Vermont both establish a "Council of Censors" separate from the other branches of government, with the task of "recommending to the legislature the repealing of such laws as appear to them to have been enacted contrary to the principles of the constitution," an institution somewhat similar to a modern constitutional court.
In 1919 the First Austrian Republic established the first dedicated constitutional court, the Constitutional Court of Austria, which however existed in name only until 10 October 1920, when the country's new constitution came into effect, upon which the court gained the power to review the laws of Austria's federal states. The 1920 Constitution of Czechoslovakia, which came into effect on 2 February 1920, was the first to provide for a dedicated court for judicial review of parliamentary laws, but the court did not convene until November 1921. The organization and competences of both courts were influenced by constitutional theories of Hans Kelsen. Subsequently, this idea of having a separate special constitutional court that only heard cases concerning the constitutionality of the national legislature's acts became known as the Austrian System, and it was subsequently adopted by many other countries e.g. Liechtenstein (1925), Greece (1927), Spain (1931), Germany (1949) etc.
See also: List of supreme courts by country
Following list consists countries with separate constitutional courts. Yet some other countries do not have separate constitutional courts, but instead delegate constitutional judicial authority to their ordinary court system, with the final decision-making power resting in the supreme ordinary court. Nonetheless, such courts are sometimes also called "constitutional courts". For example, the Supreme Court of the United States has been called the world's oldest constitutional court because it was one of the earliest courts in the world to invalidate a law as unconstitutional (Marbury v. Madison), even though it is not a separate constitutional court, hearing as it does cases not touching on the Constitution.