Summary: This study highlights the contribution made by St. Bernardine of Siena to social and political ethics. Through the virtue of caritas, translating the voluntary paupertas, of St. Francis, St. Bernardine indicates to the cives fideles a model of behaviour for the safeguarding of the res publica. On the lips of the Observant preacher, the Gospel code would become the guiding norm for the civitas as it is engaged upon the distribution of the common good, a criterion for distinguishing between licit and illicit commercial practices, for the whole of the Franciscan school of economics. Commercial goods do not an objective value, but acquire their meaning inasmuch as they are being exchanged without damaging the value of the goods, their price, and the persons who produce them, exchange them and use them. In conclusion there is presented a crucial element of reflection concerning Bernardinian civil thought in its historical dimension: How far does the community extend, to which the bonum commune is applied, in which it increases and within which it is distributed? What is the concrete horizon of civil caritas?