This chapter explores the foundations of the Fourth Republic that is a Democratic Republic (1932-1973) that is characterized by a reinforced Presidentialism, the use of extraordinary powers. It also includes a commentary about the Chilean Constitution and the opinion of the famous austrian jurist Hans Kelsen.The new social constitutionalism that is part of the twentieth century and the subsequent extension of rights is explained. Also the social function of property and its impact on the agricultural reform process and several other reforms is explained.Corporatism, the growing foreign influence and militarism are reinforced during this period.Furthermore, the Statute of Constitutional Guarantees and Salvador Allende’s socialist revolution is exposed on some its main political measures and the criticism that arise about this government. The new political parties and agents are briefly exposed and the 1973 coup d’etat that destroyed the Fourth Republic.