Notwithstanding recent interest in the study of constitutional amendment rules, there is very limited scholarship investigating the structure of formal amendment framework and little doctrinal debate on the role of upper houses, as subnational units\u2019 representatives, played in amendment processes and their capacity to strengthen the rigidity of constitutions. From an institutional framework perspective, this analysis emphasizes the rules according to which the upper houses take part in constitutional revision processes, critically assessing the advantages and disadvantaged as well as the reasons of inclusion in these procedures. In this regard, firstly, it presents the theoretical rationales for their inclusion in the constitutional amendment process; secondly, it examines the amendment rules and identifies those mechanisms which gradually structure the constitutional rigidity
