Giles of Rome was a philosopher and theologian active at the University of Paris in the second half of the thirteenth century. He was probably a student of Thomas Aquinas, who had a strong influence on Giles’ thought. Giles, however, also was a very original thinker. In metaphysics, for example, he accepted Aquinas’ view that there is a mind-independent distinction between the essence and the existence of a creature but departed from Aquinas in interpreting this distinction in a very strong sense as a distinction between two things. Furthermore, in his mature view about the role of intentional species in human cognition Giles rejected Aquinas’ account according to which such species are formal causes of cognitive acts and identified them either with the cognitive acts themselves, like in the case of the acts of the external senses, or with causal proxies for the objects of cognitive acts, like in the case of most acts of human intellectual cognition. Giles’s contribution to Aristotelian natural philosophy was very significant too, in particular to the debates about fundamental notions like those of matter, place, time, and the continuum.