This chapter investigates the main rationales and justifications of bicameralism, arguing that all modern bicameral systems are based, in their roots, on two possible ultimate justifications: the separation of powers and the protection of minorities. The chapter then explores the model of bicameralism adopted in the Italian Constitution of 1947. The analysis argues that the bicameral system of the Italian Republican Constitution is a formidable case study, as long as it is almost exclusively based on one single driver of bicameralism, namely the separation of powers. After analysing this model, the chapter explores the changing pattern of Italian bicameralism in light of the European integration process. European integration, a source of limitation of sovereignty, is considered as a key factor of the overcoming of the main justification of Italian bicameralism.