A judiciary is a number of judges mediating disputes to determine outcome. Most countries have systems of appeal courts, answering up to a supreme legal authority. In the United States, this is the Supreme Court; in Australia, the High Court; in the UK, the Supreme Court; in Germany, the Bundesverfassungsgericht; in France, the Cour de Cassation. For most European countries the European Court of Justice in Luxembourg can overrule national law, when EU law is relevant. The European Court of Human Rights in Strasbourg allows citizens of the Council of Europe member states to bring cases relating to human rights issues before it.
Some countries allow their highest judicial authority to overrule legislation they determine to be unconstitutional. For example, in Brown v. Board of Education, the United States Supreme Court nullified many state statutes that had established racially segregated schools, finding such statutes to be incompatible with the Fourteenth Amendment to the United States Constitution.
A judiciary is theoretically bound by the constitution, just as all other government bodies are. In most countries judges may only interpret the constitution and all other laws. But in common law countries, where matters are not constitutional, the judiciary may also create law under the doctrine of precedent. The UK, Finland and New Zealand assert the ideal of parliamentary sovereignty, whereby the unelected judiciary may not overturn law passed by a democratic legislature.
In communist states, such as China, the courts are often regarded as parts of the executive, or subservient to the legislature; governmental institutions and actors exert thus various forms of influence on the judiciary. In Muslim countries, courts often examine whether state laws adhere to the Sharia: the Supreme Constitutional Court of Egypt may invalidate such laws, and in Iran the Guardian Council ensures the compatibility of the legislation with the “criteria of Islam”.