The 120 Days of Sodom, or the School of Libertinage is an unfinished novel by the French writer and nobleman Donatien Alphonse François, Marquis de Sade, written in 1785 and published in 1904 after its manuscript was rediscovered. It describes the activities of four wealthy libertine Frenchmen who spend four months seeking the ultimate sexual gratification through orgies, sealing themselves in an inaccessible castle in the heart of the Black Forest with 12 accomplices, 20 designated victims and 10 servants. Four aging prostitutes relate stories of their most memorable clients whose sexual practices involved 600 "passions" including coprophilia, necrophilia, bestiality, incest, rape, and child sexual abuse. The stories inspire the libertines to engage in acts of increasing violence leading to the torture and murder of their victims, most of whom are adolescents and young women.

Donatien Alphonse François, Marquis de Sade was a French writer, libertine, political activist and nobleman best known for his libertine novels and imprisonment for sex crimes, blasphemy and pornography. His works include novels, short stories, plays, dialogues, and political tracts. Some of these were published under his own name during his lifetime, but most appeared anonymously or posthumously.