Chapter “Sade, Monism and Entropy” addresses Sade’s metaphysical commitment to entropy, displayed in his texts Justine and Juliette in particular. It addresses (i) his repudiation of materialism and egoism, (ii) his commitment to eternalism, transcendental fatalism and timelessness, and (iii) his monism and occasionalism. It considers the profound analogies between his cosmological thought and that of the pioneers of thermodynamics such as Boltzmann, Gibbs, Poincaré and Zermelo. It then evaluates the consistency and plausibility of his position.