There are many significant testimonies to the legacy of Leibniz's thinking on Peano: at least two hundred textual references and quotations from Leibnizian writings, which can be identified in his output.1 The influence of some of these suggestions in various mathematical disciplines can be recognised, above all, where Peano and his students consider and present their work as being designed to complete or to extend some of the lines of research indicated by Leibniz. Thus certain Leitmotive emerge: the desire to situate the developments of ideography in a historical context, finding in Leibniz a precursor of their work; the sharing of Leibniz's philanthropic ideals and, in particular, of his conviction of the usefulness of an international language to facilitate collaboration and communication among peoples; the inheritance of an interest in the history of mathematics, with a view to establishing the paternity of concepts, methods and symbols and lastly, the desire to take from Leibniz's work cues for the development of new results of pure and applied mathematics.