It is my purpose in this Introduction to the Constitution of the United States, Annotated to sketch rapidly certain outstanding phases of the Supreme Court's interpretation of the Constitution for the illustration they may afford of the interests, ideas, and contingencies which have from time to time influenced the Court in this still supremely important area of its powers and of the comparable factors which give direction to its work in the same field at the present time.

            As employed in this country, Constitutional Law signifies a body of rules resulting from the interpretation by a high court of a written constitutional instrument in the course of disposing of cases in which the validity, in relation to the constitutional instrument, of some act of governmental power, State or national, has been challenged. This function, conveniently labelled "Judicial Review," involves the power and duty on the part of the Court of pronouncing void any such act which does not square with its own reading of the constitutional instrument. Theoretically, therefore, it is a purely juristic product, and as such does not alter the meaning. To those who hold this theory, the Court does not elaborate the instrument, as legislative power might; it elucidates it, bringing forth into the light of day, as it were, what was in the instrument from the first.