judicial review: The power of courts to declare acts of the executive and legislature unconstitutional.  Principle is not in the Constitution but was articulated in the case: Marbury v. Madison (1803).  It is based upon the assumptions that the Constitution is the supreme law of the land, that acts contrary to the Constitution are void, and that the judiciary is the guardian or interpreter of the Constitution. Throughout American history the courts have played a major role in developing public policy by the exercise of this power.