This article discusses the contribution of Mauro Cappelletti—one of the outstanding comparative constitutional scholars of the twentieth century in Italy and worldwide—to comparative constitutional justice. Among many, three topics have been selected in this article: (i) the models of judicial review of legislation and the converging trends between the European model and the American one, (ii) the place of the judiciary in lawmaking, and (iii) the comparative method and the development of transnational law. The article reviews Cappelletti’s scholarship and explores the reasons for its lasting relevance: Cappelletti’s understanding of constitutionalism is remarkably contemporary and very inspiring for the present-day reader, notwithstanding two decades that have passed since his last book was published and the fact that the first steps of his academic activity date back to the early 1950s, i.e., over 60 years ago.