The collection of manuscript letters — about 15.000 of them — covers the time from the beginning of the 19th century until the end of the 20th century. It consists of letters to Casa Ricordi by writers, singers and composers including Giuseppe Verdi, Giacomo Puccini, Franz Liszt, Ottorino Respighi, Jules Massenet, Alfredo Casella and Luigi Nono; the librettists Luigi Illica, Giuseppe Giacosa and Arrigo Boito; the poet Gabriele d’Annunzio; and the singers Teresa Stolz, Maria Waldmann and Victor Maurel. There are also extensive further inventories from the 20th century, both manuscript and typewritten: letters by Gian Francesco Malipiero (1942—1954), Ildebrando Pizzetti (1942—1956), Vieri Tosatti (1949—1960) and Mario Zafred (1950—1956), letters from Tito I and Giulio, and numerous letters associated with specific works.
The “copialettere”, the business correspondence, form the second part of the collection of letters. They are complete from 1888 to 1962, with some gaps from 1944 to 1953. Each financial year is divided into several volumes. An index volume lists the addressees. The “copialettere” enable the reconstruction of correspondence, as was the case for the letters to Arturo Toscanini, for example.