This dissertation examines the perennial problem in philosophy and theology of reconciling divine simplicity with the plurality of divine attributes. Simplicity is a negative doctrine, according to which God lacks parts of any kind, whether physical or metaphysical. But philosophers and theologians of all three Western monotheisticreligions have upheld the truth and applicability of statements that ascribe to God various perfections, such as 'God is wise,' 'God is just,' and 'God is good.' These statements appear to violate divine simplicity, because taken individually they introduce a distinction between an attribute or property of God and the divine essence itself (for example, between God and God's goodness), and taken together they posit a plurality of attributes in God. My dissertation is a close examination of the Scholastic controversy concerning the divine attributes and the philosophical attempts to reconcile a plurality of divine attributes with the simplicity of God. After motivating the discussion by referring to early Islamic thought and contemporary philosophy of religion, I reconstruct and analyze the debate at the universities during the period 1100-1300.My thesis is that three families of solutions emerge in the medieval debate: (1) what Icall the semantic solution. According to its proponents, statements such as 'God is just' have a double signification. The primary signification is the divine essence. According to their secondary signification, they signify the plurality of God's actions in creation. So, on this solution, even if 'justice' or 'wisdom' are predicated of God, both signify only the one, simple, divine essence. (2) The Thomist solution, which claims that the plurality of attributes is not in reality but the result of an intellectual activity. The proponents of this view were split between defenders of Thomas, who maintained that the intellect in question is the human intellect, and defenders of Henry of Ghent, who argued that the divine intellect generated the attributes. (3) The realist solution, which holds that the plurality of the attributes is in reality independently of any intellect, even the divine intellect. Both God and human beings 'discover' the divine attributes already present in the divine essence.