As it comes to the classification of the written laws, the famous legal philosopher Kelsen should be remembered since he was the first jurist who made a classification showing the hierarchy of the written laws as well. The most influential legal theory of the 20th century in the Continental Europe is considered to be Kelsen’s “pure theory of law”. According to this theory, the typical legal system is founded upon a system of norms. The written laws form a part of a hierarchical system of norms, with each layer gaining authority from the previous. All the norms could be traced back through a chain of validity which is shown by a pyramid known as the Kelsen’s pyramid. At the top of this pyramid is the “Grundnorm,” namely the “Constitution” in our system. Then, the codes and statutes follow the constitution. International treaties, presidential decrees and by-laws are the other written sources in the Turkish legal system.