Participation and Substantiality in Thomas Aquinas presents a comprehensive and penetrating account of Aquinas metaphysics of creation. Its main focus is the concept of participation of being. On the basis of a detailed textual analysis a philosophical interpretation is offered of the main concepts and arguments which underlie Thomas theocentric understanding of reality.The central unifying theme of the book is the apparent tension between the notion of participation (central to the Platonic tradition) and that of substance (central to the Aristotelian tradition). The author argues that Aquinas is quite successful in bringing together in his metaphysics on the one hand the substantiality of finite beings and on the other hand their total dependency upon the divine being by way of participation.The author defends his interpretation in a critical discussion of the views on participation brought forward by well-known Aquinas scholars such as Geiger and Fabro.