Foucault's Pendulum (original title: Il pendolo di Foucault [il ˈpɛndolo di fuˈko]) is a novel by Italian writer and philosopher Umberto Eco. It was first published in 1988, with an English translation by William Weaver being published a year later.
The book is divided into segments represented by the ten Sefiroth. It is satirical, being full of esoteric references to Kabbalah, alchemy, and conspiracy theories, to the point that critic and novelist Anthony Burgess suggested that it needed an index. The pendulum of the title refers to an actual pendulum designed by French physicist Léon Foucault to demonstrate Earth's rotation, which has symbolic significance within the novel. Some believe that it refers to Michel Foucault, given the author's friendship with him, but Eco "specifically rejects any intentional reference to Michel Foucault"—this being regarded as another subtle literary joke.