This book examines Diderot's and d'Holbach's views on determinism to illuminate some of the most important debates taking place in eighteenth-century Europe. Insisting on aspects of Diderot's and d'Holbach's thought that, to date, have been given scant, if any, scholarly attention, it proposes to restore both thinkers to their rightful position in the history of philosophy. The book problematises Diderot's and d'Holbach's atheism by showing their philosophy to be deeply rooted in the Christian tradition and offers a more nuanced and historicised interpretation of the so-called "Radical Enlightenment", challenging the notions that this movement can be taken to be a perfectly coherent set of ideas and that it represents a complete break with "the old". By examining Diderot's and d'Holbach's works in tandem and without post-romantic assumptions about originality and single authorship, it argues that the two philosophers' texts should be taken as the product of a fascinating collaborative form of philosophical enquiry that perfectly reflects the sociable nature of intellectual production during the Enlightenment. The book further proposes a fresh interpretation of such crucial texts as the Systeme de la nature and Jacques le fataliste et son maitre and unveils a key web of concepts that will help researchers to better understand Enlightenment philosophy and literature as a whole.