Modern constitutional law has developed various means of supervising and guaranteeing the effective implementation of the constitution. The principal means of judicial control of constitutionality is judicial review of the constitutionality of legislation enacted by Parliament, or constitutional judicial review. This has become a dominant feature of modern constitutionalism, and recent decades have seen a global expansion of such judicial review mechanisms. This article considers the phenomenon and institution of constitutional judicial review from historical and comparative perspectives. The different models, structures and forms of constitutional judicial review are discussed with reference to the historical contexts in which they have evolved, their modes of operation and their underlying rationales. The possible tension between constitutional judicial review and democracy is also considered.