From his geometrical method to his geometrical examples; from his doctrine of reason to his explanation of bodies in motion; and from his account of the affects to his understanding of social relations, ratio is of prime importance in Spinoza's philosophy. These 11 essays explore the surprisingly varied dimensions of this unacknowledged keystone of Spinoza's thought. They take you from Spinoza's geometrical diagrams to his concepts of mind, body, the emotions, and the cosmos. It shows how Spinoza's thinking about ratio influences the concept of proportion in Gulliver's Travels, the differential ontology of Deleuze, egalitarian design for wellbeing, and the notion of an affective architecture.