This book interrogates the ontology of mathematical entities in Spinoza as a basis for addressing a wide range of interpretive issues in Spinoza epistemology—from his antiskepticism and philosophy of science to the nature and scope of reason and intuitive knowledge and the intellectual love of God. Going against recent trends in Spinoza scholarship, and drawing on various sources, including Spinoza engagements with optical theory and physics, Matthew Homan argues for a realist interpretation of geometrical figures in Spinoza; illustrates their role in a Spinozan hypothetico-deductive scientific method; and develops Spinoza mathematical examples to better illuminate the three kinds of knowledge. The result is a portrait of Spinoza epistemology as sanguine and distinctive yet at home in the new Cartesian and Galilean scientific-philosophical paradigm.