Judicial review can be understood in the context of two distinct—but parallel—legal systems, civil law and common law, and also by two distinct theories of democracy regarding the manner in which government should be organized with respect to the principles and doctrines of legislative supremacy and the separation of powers.
First, two distinct legal systems, civil law and common law, have different views about judicial review. Common-law judges are seen as sources of law, capable of creating new legal principles, and also capable of rejecting legal principles that are no longer valid. In the civil-law tradition, judges are seen as those who apply the law, with no power to create (or destroy) legal principles.
Secondly, the idea of separation of powers is another theory about how a democratic society's government should be organized. In contrast to legislative supremacy, the idea of separation of powers was first introduced by Montesquieu; it was later institutionalized in the
Differences in organizing "democratic" societies led to different views regarding judicial review, with societies based on common law and those stressing a separation of powers being the most likely to utilize judicial review. Nevertheless, many countries whose legal systems are based on the idea of legislative supremacy have learned the possible dangers and limitations of entrusting power exclusively to the legislative branch of government. Many countries with civil-law systems have adopted a form of judicial review to stem the tyranny of the majority.
Another reason why judicial review should be understood in the context of both the development of two distinct legal systems (civil law and common law) and two theories of democracy (legislative supremacy and separation of powers) is that some countries with common-law systems do not have judicial review of primary legislation. Though a common-law system is present in the
Two landmark decisions by the U.S. Supreme Court served to confirm the inferred constitutional authority for judicial review in the
As of 2014, the United States Supreme Court has held 176 Acts of the U.S. Congress unconstitutional.