This chapter addresses how Gilles Deleuze’s The Fold: Leibniz and the Baroque has affected architectural design and theory. It summarizes key concepts in The Fold, and it discusses how architects and architectural historians have drawn upon this philosophical text to analyze architectural design processes and the built environment. In The Fold, Deleuze argues that Gottfried Wilhelm Leibniz’s philosophy exemplifies the Baroque, the predominant style of art, architecture, and music created in Europe during the seventeenth and early eighteenth centuries. Leibniz’s conception of matter as forces correlates with the curvilinearity and dynamism that characterizes this style. This overview concentrates on how calculus, a mathematical method that Leibniz invented in the late seventeenth century, inspired his notions of matter, the soul, and perception. Moreover, it addresses how Deleuze interprets these concepts in The Fold, and it explains how he uses architectural examples to clarify his arguments. Shortly after The Fold was published in French in 1988, architects such as Peter Eisenman began to create designs inspired by Leibniz’s thoughts on ontology and matter. During the 1990s, Greg Lynn employed Deleuze’s reading of Leibnizian philosophy to assess contemporary architecture and design processes. This chapter discusses how his publications on “folding” architecture draw an analogy between Leibniz’s calculus-inspired notions of matter and the new digital tools that architects were using to create and manipulate forms. It also addresses critiques of “folding” architecture and digital design practices.