Which is the meaning of constitutional review for a proper assessment of subnational constitutionalism? The essay tries to answer this question by means of comparative analysis. To do so, it considers both federal systems (the United States and Germany) and regional or autonomic systems (Italy and Spain). The analysis of organs and procedures allows to draw some conclusions: the presence of a system of constitutional review at the subnational level is a crucial element for the development of an autonomous, well-grown subnational constitutional law. However, subnational constitutional courts tend to have a more complicated relation with legislative and executive bodies, as less guarantees of independence or court-overturning amendments show. Finally, subnational constitutional courts tend to develop a quite interesting case law, whose experimental features sometimes anticipate major judicial trends.