All the following letters are from the archive of Giuseppe Peano, Italian mathematician and linguist. He was elected as the director of the Akademi Internasional de Lingu Universal in 1908 after the directorships of Waldemar Rosenberger and M. A. F. Holmes. These letters are written for the most part by Rosenberger himself between 1907 and 1912. They generally concern the affairs of the Academy and linguistic questions related to the evolution of the Academy’s language. One will also find letters written in a reformed Idiom Neutral, the final form of which was published by Rosenberger in 1912 and named Reform-Neutral.