Will Moses reach the Promised Land? Will Dante get across the Styx? The Bible and The Divine Comedy are not generally thought of as cliff hangers, but that is just what they have become to millions of Italians. Each week readers rush to the newsstands—which also prominently display dozens of girlie publications—to buy magazine-like booklets that contain installments from a classic or an encyclopedia. The idea of dispensing culture in weekly dollops has brought a fortune to the three Milanese publishers who conceived it.

The Fabbri brothers—Giovanni, 43, Dino, 41, and Rino, 36—started with a small textbook company after World...