Modern constitutionalism is generally defined through the drafting of texts organizing the separation of powers. It can also be analysed as a decisive step to consider the constitution as a paramount law to be applied by the courts. This chapter proposes to compare the developments of constitutional law since the American and French revolutions with a focus on the history of judicial review. It first shows the importance of the phenomenon of constitutional adjudication and the meaning of the application of the constitution by the courts. Using new researches about the US Supreme Court, it then analyses the progress of constitutional review in 19th century America. A third section is devoted to France, contrasting constitutional instability with attempts to have the courts apply constitutional provisions. The fourth section studies the discrete steps to introduce different forms of constitutional adjudication in Europe before World War I. The fifth section revisits the work of Kelsen and the Austrian Constitutional Court in their historical context.