Diego Fratelli has edited collections of polyphonic music, both lay and sacred, by a number of Italian composers, publishing them with Rugginenti (Milan), Turris (Cremona) and for the Luca Marenzio International Festival.

Together with Paolo Portoghesi and others, he has also written a study of music and architecture in G.B.Vittone's seventeenth-century treatise, published for the "Centro Studi" in Grignasco.

He has collaborated with specialized journals and with music publishers, such as Amadeus, Ars Musici, Glossa, as well as with opera theatres for the staging of eighteenth-century music pieces (Teatro Ponchielli in Cremona, Teatro Regio in Turin). 

For the last few years he has been lecturing in a number of institutions such as the Accademia Internazionale della Musica (formerly the Scuola Civica in Milan) and the music state schools in Brescia, Florence, Lecce, Lugano, Perugia; he has also lectured in the Pontificio Istituto di Musica Sacra in Milan, teaching Renaissance and baroque music theory and praxis, choral work on original sources, ensemble music, vocal counterpoint, history of early music. 

He has also presented a number of papers at the Fondazione Cini in Venice, and organized workshops for the Early Music International Summer School in Urbino, for the Costanzo Porta Choir in Cremona, and for the music state schools in Aosta, Turin, and Venice.