This chapter discusses John Philoponus' life and work, the philosophy of the early Philoponus, and the philosophy of the later Philoponus. It presents a survey of the extant philosophical writings attributed to Philoponus, and mentions the most important other extant or partly preserved works. These include In Categorias, In Meteorologica I, and In Physica. The chapter outlines two systems that focus on exegetical policy, metaphysics, psychology and cosmology as a whole. The first prominent characteristic of the philosophy of Philoponus I is its attempt to harmonize Aristotle with Plato on the basis of Platonic metaphysics. The chapter also discusses those views of the later Philoponus which contrast with corresponding views of his Platonic period. The early Philoponus gave a non-literal interpretation of Plato's cosmogony and psychogony, and of Aristotle's criticism of them, in order to harmonize Aristotle with Plato as much as possible. The beginning and end of Philoponus' work, including Proclus' first Argument, are lost.