This present Ph.D. thesis in Constitutional Law is about stare decisis which imposes to the inferior Courts the duty of obeying and following the judicial Superior Courts precedents. This thesis is divided in two parts. The first part analyses the constitutionals principles of equality, rule of law and democratic as both justifying and legitimating factors of the adoption of the stare decisis, since they both assure coherency and consistency in the judicial decisions and reaffirm the ideal of stability and justice. The second part analyses the role played by Judicial Courts in the modern States, it describes and critically analyses the various theoretical models about the stare decisis doctrine in order to develop a coherent theory for a correct use of the doctrine and, finally, develop the institutional principles that the rule the overruling to harmonize the tensions between the needs of stability and flexibility of judicial system, that come from the demands of juridical certainty and the demands of the changing moral principles that concern to the social justice.