As the President of the Supreme Court of Israel, Aharon Barak, said, “This century is the century of judicial review”. Although this is a well known fact, judicial review is persistently under scrutiny. It is analyzed both from the political philosophy and from the legal philosophy. Since both disciplines inform Constitutional Law, sometimes judicial review is justified on the grounds of politics and sometimes it is justified on the name of the Law, obscuring its study. The lack of a method to distinguish between political philosophy based theories from legal philosophy based theories increases this problem. I propose to use the distinction between form and substance as a method. By using it, chapter one exposes the main substantive theories regarding judicial review, while chapter two exposes a classical formal legal philosophy. Chapter three exposes the distinction itself between form and substance and applies it to the examination of Marbury v. Madison, while chapter four focuses in constructing a formal justification of judicial review. The results should help shed some light about judicial review to anyone interested in Constitutional Law and Legal Theory.