This chapter is dedicated to describing how the challenges that Renaissance painters were facing while trying to represent reality as they saw it, led to a first, informal, creation of projective geometry. We look at specific paintings to extract the basic ideas that were necessary, and we show how one can build a mathematical model of painting that naturally leads to the introduction of points and lines at infinity. The necessity of representing typical religious themes such as saints’ halos leads us to the discussion of conic sections and their projective nature. To complete, so to speak, the picture, we introduce complex elements that allow a very symmetric description of plane geometry.