The "Pure Theory of Law" is the most prominent work of the Austrian philosopher and lawyer, Hans Kelsen. This book is considered to be the most complete work on the positivist and fundamentalist legal philosophy, which rejects the views of natural, sociological, and historical schools. Kelsen regard his own view to be "pure" since he claims that the laws must be purified from any psychological, biological, ethical, and theological element.

Kelsen perceives the legal order as a hierarchy or pyramid, at the top of which there is a "core norm" as the source of the legitimacy for all legal rules and norms. His another theory in this book is monotheism, which is summarized in several respects: the unity of laws and government, the unity of personal laws and objective laws, the unity of private and public laws, and the unity of national and international laws.