Constitutionality refers to the agreement with a nation's constitution, especially a law. When a law violates a constitution, it is unconstitutional. Most constitutional issues in the United States involve the Bill of Rights. These are the first 10 amendments to the US constitution. Something that is unconstitutional refers to an action by a government that violates that government's authority. Most constitutions establish the powers that a government may have. Only a government action can violate a state or federal constitution. An example is the US Constitution that guarantees that the United States may not have an official religion. This is why holiday decorations at a city hall displaying only Christian images would be unconstitutional.
Constitutionality Facts for Kids. Kiddle Encyclopedia.