 Called Le Rêve de D’Alembert (D’Alembert’s Dream), the work is in fact a trilogy of dialogues whose centerpiece provides the title. This complex text reveals some of Diderot’s most important thinking about metaphysics as it relates to biology and the life sciences. Although it was never published in Diderot’s lifetime, it was nevertheless one of his favorite works, and he gave one copy to Catherine the Great as a gift, together, significantly in terms of his understanding of the work, with a set of “Fragments” that he presented as belonging to his physiological writings. The dialogues would certainly have been considered a subversive work had they been published when they were written, and whatever Diderot’s motivations in producing it as he did, the creative complexity converges into what is without question one of the great masterpieces of Enlightenment philosophie.