1. Written documents: Constitutions can be found in written documents such as the United States Constitution, the Indian Constitution, and the Constitution of South Africa.
2. Custom and tradition: Some constitutions are based on long-standing customs and traditions that have evolved over time, such as the unwritten constitution of the United Kingdom.
3. Statutes and laws: Constitutions can also be derived from statutes and laws passed by a country's legislature, such as the Basic Law of Germany or the Constitution of Japan.
4. Judicial decisions: Constitutional principles can be established through judicial decisions, where courts interpret and apply the constitution to specific cases, such as in the United States through landmark Supreme Court cases like Brown v. Board of Education.
5. International treaties and agreements: Some constitutions incorporate principles and rights from international treaties and agreements, such as the European Convention on Human Rights influencing the constitutions of European countries.