This article explores the importance of the Casa Sonzogno publishing house for the Italian operetta market from the second half of the nineteenth century until the eve of the First World War, including its offshoot company Casa musicale Lorenzo Sonzogno. The article focuses particularly on Casa Sonzogno’s policies of importation, translation and intermedial adaptation of foreign (mainly French) light music-theatre works, especially in the context of the wider social, economic and technological environment of Milan at the turn of the twentieth century, and considers Sonzogno’s concorsi for young composers. The article then addresses the experimental activities of the Casa musicale Lorenzo Sonzogno (1909–15), notably across opera, operetta and cinema. Casa Sonzogno’s centrality to the establishment of an Italian operetta market, I argue, both highlights the crucial role of publishers in the Italian operetta industry, and offers an alternative theatrical history to familiar narratives focused on Casa Ricordi and Italian opera.